JAVA 基础知识学习23

目录

    • 目录
      • BigDecimal类
      • 练习测试
      • 简单的模拟时钟
      • 公历万年历
      • 七星彩号码生成器
      • 获取2-32之间偶数之和
      • 格式化 数字
      • 根据不同近似处理模式处理商的精度
      • 计算用户输入数值的弧度
      • 求平方根立方根和乘方并输出整数
      • 用Math类的random方法产生随机整数
      • 格式化double 型数据

BigDecimal类

BigDecimal的实现利用到了BigInteger,不同的是BigDecimal加入了小数的概念。一般的float型和Double型数据只可以用来做科学计算或工程计算,由于在商业计算中,要求数字精度比较高,所以要用到java.math.BigDecimal类。BigDecimal类支持任何精度的定点数,可以用它来精确计算货币值。

在BigDecimal类中常用的两个构造方法如下:

l         public BigDecimal(double val):实例化时将双精度型转换为BigDecimal类型

l         public BigDecimal(String val) :实例化时将字符串形式转换为BigDecimal类型

BigDecimal类型的数字可以用来做超大的浮点数的运算,比如加减乘除等,但是在所有的运算中除法是最复杂的,因为在除不尽的情况下末位小数点的处理是需要考虑的。

下面列举了BigDecimal类中实现加减乘除的方法。

l  


       public BigDecimal add(BigDecimal augend):做加法操作

l         public BigDecimal subtract(BigDecimal subtrahend):做减法操作

l         public BigDecimal multiply(BigDecimal multiplicand):做乘法操作

l         public BigDecimal divide(BigDecimal divisor,int scale,int roundingMode) //做除法操作,方法中3个参数分别代表除数、商的小数点后的位数、近似处理模式

在上述方法中,roundingMode模式有多种设置,用于返回商末位小数点的处理,这些模式的名称与含义如表1所示。

JAVA 基础知识学习23_第1张图片

下面设计一个类,这个类包括任意两个Decimal类型数字的加、减、乘、除运算方法。请读者看下面的实例。
例 在项目中创建BigDecimalDemo类,在类中分别定义add()、sub()、mul()和div()方法实现加减乘除运算,并输出运算结果。

import java.math.BigDecimal;
public class BigDecimalDemo {
      static final int location = 10;
      // 定义加法方法,参数为加数与被加数
      public static BigDecimal add(double value1, double value2) { 
            BigDecimal b1 = new BigDecimal(Double.toString(value1));        // 实例化一个Decimal对象
            BigDecimal b2 = new BigDecimal(Double.toString(value2));
            return b1.add(b2);                               // 调用加法方法
      }
      // 定义减法方法,参数为减数与被减数
      public static BigDecimal sub(double value1, double value2) { 
            BigDecimal b1 = new BigDecimal(Double.toString(value1));
            BigDecimal b2 = new BigDecimal(Double.toString(value2));
            return b1.subtract(b2);                 // 调用减法方法
      }
      // 定义乘法方法,参数为乘数与被乘数
      public static BigDecimal mul(double value1, double value2) { 
            BigDecimal b1 = new BigDecimal(Double.toString(value1));
            BigDecimal b2 = new BigDecimal(Double.toString(value2));
            return b1.multiply(b2);                 // 调用乘法方法
      }
      // 定义除法方法,参数为除数与被除数
      public static BigDecimal div(double value1, double value2) { 
            return div(value1, value2, location);            // 调用自定义除法方法
      }
      // 定义除法方法,参数分别为除数与被除数以及商小数点后的位数
      public static BigDecimal div(double value1, double value2, int b) {
            if (b < 0) {
                  System.out.println("b值必须大于等于0");
            }
            BigDecimal b1 = new BigDecimal(Double.toString(value1));
            BigDecimal b2 = new BigDecimal(Double.toString(value2));
            // 调用除法方法,商小数点后保留b位,并将结果进行四舍五入操作
            return b1.divide(b2, b, BigDecimal.ROUND_HALF_UP);
      }
      public static void main(String[] args) {
            BigDecimalDemo b = new BigDecimalDemo();
            System.out.println("两个数字相加结果:" + b.add(-7.5, 8.9));
            System.out.println("两个数字相减结果:" + b.sub(-7.5, 8.9));
            System.out.println("两个数字相乘结果:" + b.mul(-7.5, 8.9));
            System.out.println("两个数字相除结果,结果小数后保留10位:" + b.div(10, 2));
            System.out.println("两个数字相除,结果保留小数后5位:" + b.div(-7.5, 8.9, 5));
      }
}

练习测试

import java.util.Scanner;

public class MathDemo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入要计算的值");
        double value=sc.nextDouble();
        System.out.println("0.5的反正弦值:" + Math.asin(value));
        System.out.println("0.5的反余弦值:" + Math.acos(value));
        System.out.println("0.5的反正切值:" + Math.atan(value));
    }
}

Math中三角函数的参数都是弧度制的。如果指定的参数是角度,就涉及了如何将角度转换成弧度。对于反三角函数其返回值是弧度的,如果需要角度则涉及如何将弧度转换成角度。这两种情况在Math类中都提供了方法来支持。本实例将演示这两个方法的使用,代码如下:

 public class MathDemo {
    public static void main(String[] args) {
        System.out.println("弧度值0.5转换成角度值:" + Math.toDegrees(0.5));
        System.out.println("角度值30转换成弧度值:" + Math.toRadians(30));
    }
}

这两个方法是Math类提供的将角度转换成弧度和将弧度转换成角度的方法。其说明如下:

方法声明:public static double toDegrees(double angrad)

参数说明:angrad是需要转换的弧度

方法声明:public static double toRadians(double angdeg)

参数说明:angdeg是需要转换的角度

通过以上运算的结果,可以发现Java虚拟机的运算并不精确。例如,30°的正弦值应该是0.5,而sin()方法的返回值是0.49。这对于需要高精度的场合显然不理想,为此Java提供了BigInteger类,它可以完成任用精度的整数运算。本实例将使用其完成基本的四则运算。代码如下:

import java.math.BigInteger;

public class BigIntegerDemo2 {
    public static void main(String[] args) {
        BigInteger number1 = new BigInteger("5");
        BigInteger number2 = new BigInteger("10");
        System.out.println("5+10="+number1.add(number2));
        System.out.println("5 - 10 = " + number1.subtract(number2));
        System.out.println("5 * 10 = " + number1.multiply(number2));
        System.out.println("5 / 10 = " + number1.divide(number2));
        Big();

    }
     public static void Big(){
            BigInteger result = BigInteger.ONE;
            for(int i=1;i<201;i++) {
                BigInteger number = new BigInteger(new Integer(i).toString());
                result = result.multiply(number);
            }
            System.out.println(result);
        }
}

简单的模拟时钟

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.awt.Rectangle;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.util.Calendar;
import java.util.GregorianCalendar;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.UIManager;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class SimulatedClock extends JFrame {

    /**
     * 
     */
    private static final long serialVersionUID = 6800523034864043557L;
    private JPanel contentPane;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
        } catch (Throwable e) {
            e.printStackTrace();
        }
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    SimulatedClock frame = new SimulatedClock();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public SimulatedClock() {
        addWindowListener(new WindowAdapter() {
            @Override
            public void windowActivated(WindowEvent e) {
                do_this_windowActivated(e);
            }
        });
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 300, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);
    }

    public void paint(Graphics g) {
        super.paint(g);// 调用父类的paint()方法,这样能在画图时能保存外观
        Rectangle rectangle = getBounds();// 获得组件的区域
        Insets insets = getInsets();// 获得组件的边框
        int radius = 120;// 设置圆的半径是120px
        int x = (rectangle.width - 2 * radius - insets.left - insets.right) / 2 + insets.left;
        int y = (rectangle.height - 2 * radius - insets.top - insets.bottom) / 2 + insets.top;
        Point2D.Double center = new Point2D.Double(x + radius, y + radius);// 获得圆心坐标
        Point2D.Double[] scales = new Point2D.Double[60];// 用60个点保存表盘的刻度
        double angle = Math.PI / 30;// 表盘上两个点之间的夹角是PI/30
        for (int i = 0; i < scales.length; i++) {// 获得所有刻度的坐标
            scales[i] = new Point2D.Double();// 初始化点对象
            scales[i].setLocation(x + radius + radius * Math.sin(angle * i), y + radius - radius * Math.cos(angle * i));// 利用三角函数计算点的坐标
        }
        for (int i = 0; i < scales.length; i++) {// 画所有刻度
            if (i % 5 == 0) {// 如果序号是5则画成大点,这些点相当于石英钟上的数字
                g.setColor(Color.RED);
                g.fillOval((int) scales[i].x - 4, (int) scales[i].y - 4, 8, 8);
            } else {// 如果序号不是5则画成小点,这些点相当于石英钟上的小刻度
                g.setColor(Color.CYAN);
                g.fillOval((int) scales[i].x - 2, (int) scales[i].y - 2, 4, 4);
            }
        }
        Calendar calendar = new GregorianCalendar();// 创建日期对象
        int hour = calendar.get(Calendar.HOUR);// 获得当前小时数
        int minute = calendar.get(Calendar.MINUTE);// 获得当前分钟数
        int second = calendar.get(Calendar.SECOND);// 获得当前秒数
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.red);// 将颜色设置成红色
        g2d.draw(new Line2D.Double(center, scales[second]));// 绘制秒针
        BasicStroke bs = new BasicStroke(3f, BasicStroke.CAP_ROUND, BasicStroke.JOIN_MITER);
        g2d.setStroke(bs);
        g2d.setColor(Color.blue);// 将颜色设置成蓝色
        g2d.draw(new Line2D.Double(center, scales[minute]));// 绘制分针
        bs = new BasicStroke(6f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER);
        g2d.setStroke(bs);
        g2d.setColor(Color.green);// 将颜色设置成绿色
        g2d.draw(new Line2D.Double(center, scales[hour * 5 + minute / 12]));// 绘制时针
    }

    protected void do_this_windowActivated(WindowEvent e) {
        new Thread() {
            public void run() {
                while (true) {
                    repaint();// 绘制时钟
                    try {
                        Thread.sleep(1000);// 线程休眠1秒钟
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            };
        }.start();
    }
}

增加圆形表盘

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.awt.Rectangle;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.util.Calendar;
import java.util.GregorianCalendar;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.UIManager;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class SimulatedClock extends JFrame {

    /**
     * 
     */
    private static final long serialVersionUID = 6800523034864043557L;
    private JPanel contentPane;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
        } catch (Throwable e) {
            e.printStackTrace();
        }
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    SimulatedClock frame = new SimulatedClock();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public SimulatedClock() {
        addWindowListener(new WindowAdapter() {
            @Override
            public void windowActivated(WindowEvent e) {
                do_this_windowActivated(e);
            }
        });
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 300, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);
    }
    public void paint(Graphics g) {
        super.paint(g);// 调用父类的paint()方法,这样能在画图时能保存外观
        Rectangle rectangle = getBounds();// 获得组件的区域
        Insets insets = getInsets();// 获得组件的边框
        int radius = 120;// 设置圆的半径是120px
        int x = (rectangle.width - 2 * radius - insets.left - insets.right) / 2 + insets.left;
        int y = (rectangle.height - 2 * radius - insets.top - insets.bottom) / 2 + insets.top;
        Point2D.Double center = new Point2D.Double(x + radius, y + radius);// 获得圆心坐标
        g.drawOval(x, y, 2 * radius, 2 * radius);// 绘制圆形
        Point2D.Double[] scales = new Point2D.Double[60];// 用60个点保存表盘的刻度
        double angle = Math.PI / 30;// 表盘上两个点之间的夹角是PI/30
        for (int i = 0; i < scales.length; i++) {// 获得所有刻度的坐标
            scales[i] = new Point2D.Double();// 初始化点对象
            scales[i].setLocation(x + radius + radius * Math.sin(angle * i), y + radius - radius * Math.cos(angle * i));// 利用三角函数计算点的坐标
        }
        for (int i = 0; i < scales.length; i++) {// 画所有刻度
            if (i % 5 == 0) {// 如果序号是5则画成大点,这些点相当于石英钟上的数字
                g.setColor(Color.RED);
                g.fillOval((int) scales[i].x - 4, (int) scales[i].y - 4, 8, 8);
            } else {// 如果序号不是5则画成小点,这些点相当于石英钟上的小刻度
                g.setColor(Color.CYAN);
                g.fillOval((int) scales[i].x - 2, (int) scales[i].y - 2, 4, 4);
            }
        }
        Calendar calendar = new GregorianCalendar();// 创建日期对象
        int hour = calendar.get(Calendar.HOUR);// 获得当前小时数
        int minute = calendar.get(Calendar.MINUTE);// 获得当前分钟数
        int second = calendar.get(Calendar.SECOND);// 获得当前秒数
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.red);// 将颜色设置成红色
        g2d.draw(new Line2D.Double(center, scales[second]));// 绘制秒针
        BasicStroke bs = new BasicStroke(3f, BasicStroke.CAP_ROUND, BasicStroke.JOIN_MITER);
        g2d.setStroke(bs);
        g2d.setColor(Color.blue);// 将颜色设置成蓝色
        g2d.draw(new Line2D.Double(center, scales[minute]));// 绘制分针
        bs = new BasicStroke(6f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER);
        g2d.setStroke(bs);
        g2d.setColor(Color.green);// 将颜色设置成绿色
        g2d.draw(new Line2D.Double(center, scales[hour * 5 + minute / 12]));// 绘制时针
    }


    protected void do_this_windowActivated(WindowEvent e) {
        new Thread() {
            public void run() {
                while (true) {
                    repaint();
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            };
        }.start();
    }
}

公历万年历

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DateFormatSymbols;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;

import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.ListSelectionModel;
import javax.swing.SwingConstants;
import javax.swing.UIManager;
import javax.swing.border.EmptyBorder;
import javax.swing.table.DefaultTableModel;

public class PermanentCalendar extends JFrame {

    /**
     * 
     */
    private static final long serialVersionUID = 3169863775528020253L;
    private JTable table;
    private JLabel currentMonthLabel;
    private Calendar calendar = new GregorianCalendar();
    private JPanel contentPane;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
        } catch (Throwable e) {
            e.printStackTrace();
        }
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    PermanentCalendar frame = new PermanentCalendar();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public PermanentCalendar() {
        setTitle("\u516C\u5386\u4E07\u5E74\u5386");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 282);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);

        JPanel YMPanel = new JPanel();
        contentPane.add(YMPanel, BorderLayout.NORTH);
        YMPanel.setLayout(new GridLayout(1, 3, 5, 10));

        JPanel lastMonthPanel = new JPanel();
        YMPanel.add(lastMonthPanel);

        JButton lastMonthButton = new JButton("\u4E0A\u4E2A\u6708");
        lastMonthButton.setFont(new Font("微软雅黑", Font.PLAIN, 16));
        lastMonthButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                do_lastMonthButton_actionPerformed(e);
            }
        });
        lastMonthPanel.add(lastMonthButton);

        JPanel currentMonthPanel = new JPanel();
        YMPanel.add(currentMonthPanel);
        currentMonthPanel.setLayout(new BoxLayout(currentMonthPanel, BoxLayout.X_AXIS));

        currentMonthLabel = new JLabel("");
        currentMonthLabel.setFont(new Font("微软雅黑", Font.PLAIN, 20));
        currentMonthLabel.setHorizontalAlignment(SwingConstants.CENTER);
        currentMonthPanel.add(currentMonthLabel);

        JPanel nextMonthPanel = new JPanel();
        YMPanel.add(nextMonthPanel);

        JButton nextMonthButton = new JButton("\u4E0B\u4E2A\u6708");
        nextMonthButton.setFont(new Font("微软雅黑", Font.PLAIN, 16));
        nextMonthButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                do_nextMonthButton_actionPerformed(e);
            }
        });
        nextMonthPanel.add(nextMonthButton);

        JScrollPane scrollPane = new JScrollPane();
        contentPane.add(scrollPane, BorderLayout.CENTER);

        table = new JTable();
        table.setFont(new Font("微软雅黑", Font.PLAIN, 18));
        table.getTableHeader().setFont(new Font("微软雅黑", Font.PLAIN, 20));
        table.setRowHeight(25);
        table.setCellSelectionEnabled(true);
        table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        scrollPane.setViewportView(table);

        currentMonthLabel.setText(updateLabel(0));
        updateTable(calendar);
    }

    private void updateTable(Calendar calendar) {
        String[] weeks = new DateFormatSymbols().getShortWeekdays();// 获得表示星期的字符串数组
        String[] realWeeks = new String[7];// 新建一个数组来保存截取后的字符串
        for (int i = 1; i < weeks.length; i++) {// weeks数组第一个元素是空字符串,因此从1开始循环
            realWeeks[i - 1] = weeks[i].substring(2, 3);// 获得字符串的最后一个字符
        }
        int today = calendar.get(Calendar.DATE);// 获得当前日期
        int monthDays = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);// 获得当前月的天数
        calendar.set(Calendar.DAY_OF_MONTH, 1); // 将时间设置为本月第一天
        int weekday = calendar.get(Calendar.DAY_OF_WEEK);// 获得本月第一天是星期几
        int firstDay = calendar.getFirstDayOfWeek(); // 获得当前地区星期的起始日
        int whiteDay = weekday - firstDay; // 这个月第一个星期有几天被上个月占用
        Object[][] days = new Object[6][7];// 新建一个二维数组来保存当前月的各天
        for (int i = 1; i <= monthDays; i++) {// 遍历当前月的所有天并将其添加的二维数组中
            days[(i - 1 + whiteDay) / 7][(i - 1 + whiteDay) % 7] = i;
        }// 数组的第一维表示一个月中各个星期,第二位表示一个星期中各个天
        DefaultTableModel model = (DefaultTableModel) table.getModel();// 获得当前表格的模型
        model.setDataVector(days, realWeeks);// 给表格模型设置表头和表体
        table.setModel(model);// 更新表格模型
        table.setRowSelectionInterval(0, (today - 1 + whiteDay) / 7);// 设置选择的行
        table.setColumnSelectionInterval(0, (today - 1 + whiteDay) % 7);// 设置选择的列
    }

    private String updateLabel(int increment) {
        calendar.add(Calendar.MONTH, increment);// 将当前月份增加increment月
        SimpleDateFormat formatter = new SimpleDateFormat("yyyy年MM月");// 设置字符串格式
        return formatter.format(calendar.getTime());// 获得指定格式的字符串
    }

    protected void do_lastMonthButton_actionPerformed(ActionEvent e) {
        currentMonthLabel.setText(updateLabel(-1));
        updateTable(calendar);
    }

    protected void do_nextMonthButton_actionPerformed(ActionEvent e) {
        currentMonthLabel.setText(updateLabel(1));
        updateTable(calendar);
    }
}

七星彩号码生成器

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
import javax.swing.UIManager;
import javax.swing.border.EmptyBorder;

public class SevenStar extends JFrame {

    /**
     * 
     */
    private static final long serialVersionUID = 6787592245621788484L;
    private JPanel contentPane;
    private JTextField textField;
    private JTextArea textArea;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
        } catch (Throwable e) {
            e.printStackTrace();
        }
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    SevenStar frame = new SevenStar();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public SevenStar() {
        setTitle("\u4E03\u661F\u5F69\u53F7\u7801\u751F\u6210\u5668");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);

        JPanel panel = new JPanel();
        contentPane.add(panel, BorderLayout.NORTH);
        panel.setLayout(new GridLayout(1, 2, 5, 5));

        JLabel label = new JLabel("\u8BF7\u8F93\u5165\u53F7\u7801\u4E2A\u6570\uFF1A");
        label.setFont(new Font("微软雅黑", Font.PLAIN, 18));
        label.setHorizontalAlignment(SwingConstants.CENTER);
        panel.add(label);

        textField = new JTextField();
        textField.setFont(new Font("微软雅黑", Font.PLAIN, 18));
        panel.add(textField);
        textField.setColumns(10);

        JPanel buttonPanel = new JPanel();
        contentPane.add(buttonPanel, BorderLayout.SOUTH);

        JButton button = new JButton("\u751F\u6210\u53F7\u7801");
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                do_button_actionPerformed(e);
            }
        });
        button.setFont(new Font("微软雅黑", Font.PLAIN, 18));
        buttonPanel.add(button);

        JScrollPane scrollPane = new JScrollPane();
        contentPane.add(scrollPane, BorderLayout.CENTER);

        textArea = new JTextArea();
        textArea.setFont(new Font("微软雅黑", Font.PLAIN, 18));
        scrollPane.setViewportView(textArea);
    }

    protected void do_button_actionPerformed(ActionEvent e) {
        int times = Integer.parseInt(textField.getText());// 获得用户输入的需要生成的中奖号码个数
        StringBuilder sb = new StringBuilder();// 利用StringBuilder类保存彩票中奖号码
        for (int i = 0; i < times; i++) {
            int number = new Random().nextInt((int) Math.pow(10, 7));// 生成随机数
            String luckNumber = "" + number;
            while (luckNumber.length() < 7) {
                luckNumber = "0" + luckNumber;// 如果随机数长度不够7位用0补齐
            }
            sb.append(luckNumber + "\n");
        }
        textArea.setText(sb.toString());// 显示生成的中奖号码
    }
}

获取2-32之间偶数之和

public class RandomTest {

    /**
     * @param args
     *            获取2到32之间的6个偶数,并且求这6个偶数的和
     */
    public static double EvenNum(double num1, double num2) {
        double s = 0;
        int[] j = new int[6];
        Random cres = new Random();
        for (int w = (int) num1, i = 0; w <= (int) num2; w += 2) {
            j[i] = cres.nextInt((int) num2);
            if (j[i] != 0 && j[i] % 2 == 0) {
                System.out.println(j[i]);
                s += j[i];
                i++;
            }
            if (i == 6)
                break;
        }
        return s;
    }

    public static double EvenNum2(double num1, double num2) {
        double s = 0;
        int[] j = new int[6];
        for (int i = 0, w = 0; i < 20; i++) {
            j[w] = (int) num1 + (int) (Math.random() * (num2 - num1));
            if (j[w] != 0 && j[w] % 2 == 0) {
                System.out.println("打印2到32之间的偶数(不包括32)" + j[w]);
                s += j[w];
                w++;
            }
            if (w == 6)
                break;
        }
        return s;
    }

    public static void main(String[] args) {
        System.out.println("和为:" + EvenNum2(2, 32));
    }

}

格式化 数字

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.border.LineBorder;

public class NumberFormateDemo extends JFrame {
    private JTextArea infoArea;
    private JTextField numberField;
    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    NumberFormateDemo frame = new NumberFormateDemo();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
    /**
     * 创建窗体的构造方法
     */
    public NumberFormateDemo() {
        super();
        final BorderLayout borderLayout = new BorderLayout(10,10);
        getContentPane().setLayout(borderLayout);
        setBounds(100, 100, 348, 225);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        final JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());
        getContentPane().add(panel, BorderLayout.NORTH);
        final JLabel label = new JLabel();
        label.setText("请输入要格式化的数字:");
        panel.add(label, BorderLayout.WEST);
        numberField = new JTextField();                 // 创建数字文本框
        numberField.setText("60");          // 演示数字
        panel.add(numberField);
        final JButton button = new JButton();           // 创建确定按钮
        button.addActionListener(new ActionListener() { // 添加事件监听器
            public void actionPerformed(final ActionEvent e) {
                do_button_actionPerformed(e);
            }
        });
        button.setText("确定");
        panel.add(button, BorderLayout.EAST);
        infoArea = new JTextArea();                     // 创建文本域组件
        infoArea.setFont(new Font("宋体", Font.PLAIN, 15));   // 设置字体
        infoArea.setBorder(new LineBorder(Color.black, 1, false));
        infoArea.setEditable(false);                    // 禁止编辑
        getContentPane().add(infoArea);
        setTitle("格式化数字");
    }
    /**
     * 确定按钮的事件处理方法
     * @param e 动作事件
     */
    protected void do_button_actionPerformed(final ActionEvent e) {
        String text = numberField.getText();
        if(text==null||text.isEmpty()){                 // 如果没有输入数字
            infoArea.setText("请输入数字");              // 显示提示信息
            return;                                     // 结束该方法
        }
        double number=0;
        try {
            number = Double.parseDouble(text.trim());   // 字符串转换为数字
        } catch (NumberFormatException e1) {
            infoArea.setText("请输入正确的数字");       // 显示提示信息
            return;                                     // 结束该方法
        }
        infoArea.setText("");
        DecimalFormat dmf=new DecimalFormat();          // 创建数字格式化对象
        addRmbFormat(number, dmf);                      // 格式化为人民币格式
        grouping3(number, dmf);                         // 3位分组
        grouping4(number, dmf);                         // 4为分组     
        keep6(number, dmf);                             // 强制保留6位小数 
        percent(number, dmf);                           // 百分比格式输出
    }
    /**
     * 百分比格式输出
     * @param number 组字
     * @param dmf 数字格式化对象
     */
    private void percent(double number, DecimalFormat dmf) {
        dmf.applyPattern("百分比:#.00%\n");
        String numStr = dmf.format(number);
        infoArea.append(numStr);
    }   

    /**
     * 强制保留6位小数
     * @param number 组字
     * @param dmf 数字格式化对象
     */
    private void keep6(double number, DecimalFormat dmf) {
        String numStr;
        dmf.applyPattern("强制保留6位小数:#.000000\n");
        numStr = dmf.format(number);
        infoArea.append(numStr);
    }

    /**
     * 按4为数字分组
     * @param number 组字
     * @param dmf 数字格式化对象
     */
    private void grouping4(double number, DecimalFormat dmf) {
        dmf.setGroupingUsed(true);
        dmf.setGroupingSize(4);
        String grouping4 = "按4为数字分组:" + dmf.format(number) + "\n";
        infoArea.append(grouping4);
        dmf.setGroupingUsed(false);
    }

    /**
     * 按3为数字分组
     * @param number 组字
     * @param dmf 数字格式化对象
     */
    private void grouping3(double number, DecimalFormat dmf) {
        dmf.setGroupingUsed(true);
        dmf.setGroupingSize(3);
        dmf.applyPattern("");
        String grouping3 = "按3为数字分组:" + dmf.format(number) + "\n";
        infoArea.append(grouping3);
        dmf.setGroupingUsed(false);
    }   
    /**
     * 人名币格式输出
     * @param number 组字
     * @param dmf 数字格式化对象
     */
    private void addRmbFormat(double number, DecimalFormat dmf) {
        dmf.applyPattern("人民币:¥#.00元\n");
        String RMB = dmf.format(number);
        infoArea.append(RMB);
    }
}

根据不同近似处理模式处理商的精度

public class UseCase {

    /**
     * @param args
     */
    public static BigDecimal div(double value1,double value2,int b,int r){
        if(b<0){
            System.out.println("b值必须大于等于0");
        }
        BigDecimal b1=new BigDecimal(Double.toString(value1));
        BigDecimal b2=new BigDecimal(Double.toString(value2));
        return b1.divide(b2,b,r);
    }
    public static void main(String[] args) {    
        UseCase u=new UseCase();
        System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_CEILING));
        System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_DOWN));
        System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_FLOOR));
        System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_HALF_DOWN));
        System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_HALF_EVEN));
        System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_HALF_UP));
        System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_UP));

    }

}

计算用户输入数值的弧度

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.border.LineBorder;

public class AccountRadian extends JFrame {
    private JTextArea infoArea;
    private JTextField numberField;
    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                    AccountRadian frame = new AccountRadian();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
    /**
     * 创建窗体的构造方法
     */
    public AccountRadian() {
        super();
        final BorderLayout borderLayout = new BorderLayout(10,10);
        getContentPane().setLayout(borderLayout);
        setBounds(100, 100, 348, 225);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        final JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());
        getContentPane().add(panel, BorderLayout.NORTH);
        final JLabel label = new JLabel();
        label.setText("请输入要计算弧度的数字:");
        panel.add(label, BorderLayout.WEST);
        numberField = new JTextField();                 // 创建数字文本框
        numberField.setText("90");          // 演示数字
        panel.add(numberField);
        final JButton button = new JButton();           // 创建确定按钮
        button.addActionListener(new ActionListener() { // 添加事件监听器
            public void actionPerformed(final ActionEvent e) {
                do_button_actionPerformed(e);
            }
        });
        button.setText("确定");
        panel.add(button, BorderLayout.EAST);
        infoArea = new JTextArea();                     // 创建文本域组件
        infoArea.setFont(new Font("宋体", Font.PLAIN, 15));   // 设置字体
        infoArea.setBorder(new LineBorder(Color.black, 1, false));
        infoArea.setEditable(false);                    // 禁止编辑
        getContentPane().add(infoArea);     
        setTitle("格式化数字");
    }
    /**
     * 确定按钮的事件处理方法
     * @param e 动作事件
     */
    protected void do_button_actionPerformed(final ActionEvent e) {
        String text = numberField.getText();
        if(text==null||text.isEmpty()){                 // 如果没有输入数字
            infoArea.setText("请输入数字");              // 显示提示信息
            return;                                     // 结束该方法
        }
        double number=0;
        try {
            number = Double.parseDouble(text.trim());   // 字符串转换为数字
        } catch (NumberFormatException e1) {
            infoArea.setText("请输入正确的数字");       // 显示提示信息
            return;                                     // 结束该方法
        }
        infoArea.setText("");
        percent(number);        
        addRmbFormat(number);                       
        grouping3(number);                          
        grouping4(number);                          
        keep6(number);                              

        getRadian(number);
    }
    /**
     * 计算某数的三角正弦值
     */
    private void percent(double number) {
        Double doub = Math.sin(number); 
        infoArea.append("该数的正弦值是:"+doub+"\n");
    }   

    /**
     * 获取余弦值
     */
    private void keep6(double number) {
        double doub = Math.cos(number);
        infoArea.append("该数的余弦值是:"+doub+"\n");
    }

    /**
     * 获取某数的正切值
     */
    private void grouping4(double number) {
        double doub = Math.tan(number);
        infoArea.append("该数的正切值是:"+doub+"\n");

    }

    /**
     * 获取某数的反正弦值
     */
    private void grouping3(double number) {
        double doub = Math.asin(number);
        infoArea.append("该数的反正弦值是:"+doub+"\n");

    }   
    /**
     * 获取某数的反余弦值
     */
    private void addRmbFormat(double number) {
        double doubl = Math.acos(number);
        infoArea.append("该数的反余弦值是:"+doubl+"\n");
    }
    /**
     * 获取某数的反余弦值
     */
    private void getRadian(double number) {
        double doubl = Math.toRadians(number);
        infoArea.append("该数的弧度是:"+doubl);
    }
}

求平方根立方根和乘方并输出整数

public class Example {
    public static void main(String[] args) {
        double pfg=0;       
        double lfg=0;           //存放立方根的变量
        double cf=0;            //存放乘方的变量
        //求出5000的平方根,并转换为与结果最接近的整数
        pfg=Math.rint(Math.sqrt(5000)); 
        //求出5000的立方根,并转换为与结果最接近的整数
        lfg=Math.rint(Math.cbrt(5000));
        //求出1.33的立方,并转换为与结果最接近的整数
        cf=Math.rint(Math.pow(1.33,3));
        System.out.println("5000的平方根是:"+pfg);
        System.out.println("5000的立方根是:"+lfg);
        System.out.println("1.33的立方是:"+cf);
    }

}

用Math类的random方法产生随机整数

public class Example {
    public static void main(String[] args) {
        // 产生0(含0)~100(不含100)之间的随机整数
        int result = (int) (Math.random() * 100);
        System.out.println("产生0(含0)~100(不含100)之间的随机整数:" + result);
        // 产生1(含1)~100(含100)之间的随机整数
        result = (int) (Math.random() * 100 + 1);
        System.out.println("产生1(含1)~100(含100)之间的随机整数" + result);
        // 产生15(含15)~70(含70)之间的随机整数
        result = (int) (Math.random() * 56 + 15);
        System.out.println("产生15(含15)~70(含70)之间的随机整数" + result);
    }
}

格式化double 型数据

import java.text.DecimalFormat;
public class Example {
    public static void main(String[] args) {
        double num=123456789.123456;
        //实例化DecimalFormat对象
        DecimalFormat format=new DecimalFormat("###,###,###.####");
        String str=format.format(num);              //将数字进行格式化
        System.out.println(str);                            //输出格式化的内容
    }
}

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