2024/1/26

常用类

今天上课有点懒，没有做笔记，只有代码

大家自行观看（狗头保命）

String类

package String;

/**
 * @Author: zh
 * @Description:
 * @Date Created in 2024-01-26 15:40
 * @Modified By:
 */
public class String01 {

    public static void main(String[] args) {
        String str = "abc";
        String str1 = "123";
        System.out.println(str == str1);

        String str2 = new String("abc");
        System.out.println(str == str2);
        String str3 = new String("abc");
        System.out.println(str2 == str3);

        String str4 = "abc";
        System.out.println(str == str4);//常量池（原理）
    }
}

package String;

/**
 * @Author: 张辉
 * @Description:
 * @Date Created in 2024-01-26 16:02
 * @Modified By:
 */
public class String02 {
    public static void main(String[] args) {
        String s = "  zhanghui NB ";
        String s1 = "NB";
        System.out.println(s.length());
        System.out.println(s.charAt(3));
        System.out.println(s.contains("NB"));
        System.out.println(s.toLowerCase());
        System.out.println(s.toUpperCase());
        System.out.println(s.trim());
        System.out.println(s.startsWith("zh"));
        System.out.println(s.endsWith("NB "));
        System.out.println(s.codePointAt(3));
        System.out.println(s.codePointBefore(3));
        System.out.println(s.compareTo(s1));
        System.out.println(s.indexOf("NB"));

        byte[] nb = {102,117,99,107,5,6};
        String n = new String(nb,0,4);
        System.out.println(n);
    }
}

StringBuilder

package String;

/**
 * @Author: 张辉
 * @Description:
 * @Date Created in 2024-01-26 17:01
 * @Modified By:
 */
public class StringBuilder01 {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        StringBuilder sb1 = new StringBuilder("what can i say!");
        System.out.println(sb.capacity());
        System.out.println(sb1.capacity());

        sb1.insert(14," manba out");
        System.out.println(sb1);
        System.out.println(sb1.append("heihei"));

        System.out.println(sb1.replace(16,26,"别say了！"));
        System.out.println(sb1.reverse());
        System.out.println(sb1.indexOf("ie"));
    }
}

Object类

package Object.Student;

import java.util.Objects;

public class Student {
    private String name;
    private int age;

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
    /*@Override
    public boolean equals(Object o){
        Student student = (Student)o;
        return this.getAge()== student.getAge();

    }*/
   /* @Override
    public boolean equals(Object o){
        //表示两个引用指向同一个地址
        if(this == o){
            return true;
        }
        if(null == o){
            return false;
        }
        if(o instanceof Student){
            Student student = (Student)o;
            if(this.getName().equals(student.getName())&&this.getAge() ==student.getAge()){
                return true;
            }
        }
        return false;
    }*/

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return age == student.age &&
                Objects.equals(name, student.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }


    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public Student() {
    }
}

package Object.Student;



public class StudentTest {
    public static void main(String[] args) {
        Student student = new Student("zh",20);
        //Object中的toString方法默认返回调用类的字符串形式
        System.out.println(student);
        Student student1 = new Student("zh",20);
        System.out.println(student1);
        System.out.println(student.equals(student1));
    }
}

Bigdecimal

package Object.Bigdecimal;

import java.math.BigDecimal;

public class Bigdecimal01 {
    public static void main(String[] args) {
        double a = 0.1 + 0.2;
        System.out.println(a);
        BigDecimal bd =new BigDecimal("0.3");
        BigDecimal bd1 = new BigDecimal("0.1");
        //加
        System.out.println(bd.add(bd1));
        //减
        System.out.println(bd.subtract(bd1));
        //乘
        System.out.println(bd.multiply(bd1));
        //除
        System.out.println(bd.divide(bd1));
        //四舍五入
        System.out.println(bd.divide(bd1,BigDecimal.ROUND_HALF_UP));
    }
}

Interger

package Object;

public class Interger01 {
    public static void main(String[] args) {
        Integer it = new Integer(10);
        System.out.println(it);
        //讲Integer类型的对象，转变为int的数值，需要手动拆箱
        int i = it.intValue();
        System.out.println(i);
        //讲int类型的对象，转变为Integer的数值，需要手动装箱
        Integer integer = Integer.valueOf(i);
        System.out.println(integer);
        Integer it1 = new Integer("20");
        System.out.println(it1);
        //JDK1.5开始提供自动装箱和拆箱的机制
        Integer w = 12;
        int w1 = w;
        System.out.println(w+" "+w1);

        String s = "123";
        int w2 = Integer.parseInt(s);
        System.out.println(w2);
    }
}

 可变参数

/**
 * @Author: 张辉
 * @Description:
 * @Date Created in 2024-01-26 18:02
 * @Modified By:
 */
public class Easy {

    public static int add(int...a){
        int sum = 0;
        for(int i:a){
            sum += i;
        }
        return sum;
    }

    public static void main(String[] args) {
        int a=1;
        int b=2;
        System.out.println(add(a,b));
    }
}

Date

package Date;

import java.util.Date;

/**
 * @Author: 张辉
 * @Description:
 * @Date Created in 2024-01-26 17:46
 * @Modified By:
 */
public class Date01 {
    public static void main(String[] args) {
        Date date = new Date();
        System.out.println(date);
        Date da = new Date(10000);
        System.out.println(da);
        System.out.println(date.getTime());
        da.setTime(1000);
        System.out.println(da);
    }
}

package Date;

import com.sun.xml.internal.ws.api.model.wsdl.WSDLOutput;

import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * @Author: 张辉
 * @Description:
 * @Date Created in 2024-01-26 17:52
 * @Modified By:
 */
public class Date02 {
    public static void main(String[] args) {
        Date date = new Date();
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String format = simpleDateFormat.format(date);
        System.out.println(format);
    }
}

LocalDate

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;

/**
 * @Author: zh
 * @Description:
 * @Date Created in 2024-01-26 18:52
 * @Modified By:
 */
public class LocalDate01 {
    public static void localDate() {
        LocalDate yyyyMMdd = LocalDate.now();
        LocalTime HHmmssSSS = LocalTime.now();
        LocalDateTime yyyyMMddHmmss = LocalDateTime.now();
        System.out.println(yyyyMMdd);
        System.out.println(HHmmssSSS);
        System.out.println(yyyyMMddHmmss);

    }
    public static void main(String[] args) {
        localDate();
    }
}

setdate

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;

/**
 * @Author: myj
 * @Description:
 * @Date Created in 2024-01-26 19:03
 * @Modified By:
 */
public class SetDate01 {
    public static void setdate(){
        LocalDate yyyyMMdd = LocalDate.of(1931,9,18);
        LocalTime HHmmssSSS = LocalTime.of(9,9,9);
        LocalDateTime yyyyMMddHHmmssSSS = LocalDateTime.of(1931,9,18,0,0);
        System.out.println("勿忘"+yyyyMMdd);
        System.out.println(HHmmssSSS);
        System.out.println(yyyyMMddHHmmssSSS);
    }

    public static void main(String[] args) {
        setdate();
    }
}

DirectDesignationTime

import java.time.LocalDate;
import java.util.Date;

/**
 * @Author: zh
 * @Description:
 * @Date Created in 2024-01-26 19:17
 * @Modified By:
 */
public class DirectDesignationTime {
    public static void DirectDesignationTime(){
        LocalDate yMd = LocalDate.now();
        System.out.println(yMd);
        LocalDate addDay = yMd.plusDays(4);
        System.out.println(addDay);

        LocalDate directDesignationDate = yMd.withDayOfMonth(20);
        System.out.println(directDesignationDate);

        LocalDate directDesignationYearDate = yMd.withDayOfYear(20);
        System.out.println(directDesignationYearDate);

        LocalDate directDesignationYear = yMd.withYear(2000);
        System.out.println(directDesignationYear);

        LocalDate directDesignationMonth = yMd.withMonth(6);
        System.out.println(directDesignationMonth);

    }

    public static void main(String[] args) {
        DirectDesignationTime();
    }
}

LessOrAddDate

import java.time.LocalDate;
import java.time.LocalTime;

/**
 * @Author: zh
 * @Description:
 * @Date Created in 2024-01-26 19:09
 * @Modified By:
 */
public class LessOrAddDate {
    public static void LessOrAddDate(){
        LocalDate yMd = LocalDate.now();
        System.out.println(yMd);
        LocalDate addOneDay = yMd.plusDays(1);//添加一日
        System.out.println(addOneDay);
        LocalDate addOneMonths = yMd.plusMonths(1);//添加一月
        System.out.println(addOneMonths);
        LocalDate addOneYears = yMd.plusYears(1);//添加一年
        System.out.println(addOneYears);
        LocalDate addOneWeeks = yMd.plusWeeks(1);//添加一周
        System.out.println(addOneWeeks);
        LocalDate delOneDay = yMd.minusDays(1); //减去一日
        System.out.println(delOneDay);
        LocalDate delOneMonths = yMd.minusMonths(1);//减去一月
        System.out.println(delOneMonths);
        LocalDate delOneYears = yMd.minusYears(1);//减去一年
        System.out.println(delOneYears);
        LocalDate delOneWeeks = yMd.minusWeeks(1);//减去一周
        System.out.println(delOneWeeks);

    }

    public static void main(String[] args) {
        LessOrAddDate();
    }
}