J2se练习1

package Study;

import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

public class MyStudy1 {

/**
 * 数组 一维数组声明方式:int a[],int[] a;声明时不能指定长度int a[5]
 * 基本数据类型：数组初始值不同。引用数据类型则都是null。数组有length属性 多维数组 声明方式:int[][] arr = new
 * int[3][3]; int[][] arr = new int[3][];不可以写成int[][] arr = new int[][3];
 * int[][] arr = new int[][]{{1,2},{3,4}};
 */
public static void main(String[] args) {
    // showA_Z();
    // showA_Number();
    // showFeb();
    // showSort();
    // showSum();
    // showInsert();
    // showDiff();
    // showExch();
    // showMove();
    // showMulExch();
    // showZero();
    showMax();
}

private static void showMax() {
    // 定义一个N*N二维数组，从键盘上输入值，找出每行中最大值组成一个一维数组并输出；
    int[][] a = { { 1, 2, 3, 4 }, { 5, 6, 9, 8 }, { 9, 10, 18, 12 }, { 13, 14, 15, 16 } };
    int[] c = new int[4];int m = 0;
    for (int i = 0; i < a.length; i++) {
        int max = a[i][0];
        System.out.println(max);
        for (int j = 0; j < a[i].length; j++) {
            if (max < a[i][j])
                max = a[i][j];
            m++;
            if (m % 4 == 0)
                c[i] = max;
        }
    }
    System.out.println(Arrays.toString(c));
}

private static void showZero() {
    // 定义一个3行4列的二维数组，逐个从键盘输入值，将左下三角的值清0
    int[][] a = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 } };
    for (int i = 0; i < a.length; i++) {
        for (int j = 0; j < a[i].length; j++) {
            if (j <= i)
                a[i][j] = 0;
        }
        System.out.println();
    }
    System.out.println("清零后:");
    for (int i = 0; i < a.length; i++) {
        for (int j = 0; j < a[i].length; j++)
            System.out.print(a[i][j] + " ");
        System.out.println();
    }
}

private static void showMulExch() {
    // 定义一个4行4列的二维数组，逐个从键盘输入值，然后将第1行和第4行的数据进行交换，将第2行和第3行的数据进行交换
    int[][] a = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 }, { 13, 14, 15, 16 } };
    int b = 0;
    System.out.println("交换前:");
    for (int i = 0; i < a.length; i++) {
        for (int j = 0; j < a[i].length; j++)
            System.out.print(a[i][j] + " ");
        System.out.println();
    }
    System.out.println("交换后:");
    for (int j = 0; j < 4; j++) {
        b = a[0][j];// 1 2 3 4
        a[0][j] = a[a.length - 1][j];
        a[a.length - 1][j] = b;
    }
    for (int i = 0; i < a.length; i++) {
        for (int j = 0; j < a[i].length; j++)
            System.out.print(a[i][j] + " ");
        System.out.println();
    }
}

private static void showMove() {
    // 有n个整数，使其前面各数顺序向后移m个位置，最后m个数变成最前面的m个数
    int[] a = { 1, 2, 3, 4, 5, 6 };
    int m = 2, q = 0, k = 0;
    int[] b = new int[m];
    for (int j = 0; j < b.length; j++) {
        b[j] = a[j];
        System.out.print("b:" + b[j] + " ");// 1 2
    }
    for (int i = m; i < a.length; i++) {
        a[k] = a[i];
        k++;
        System.out.print(k + " ");
    }
    for (int n = m; n > 0; n--) {
        a[a.length - n] = b[q];
        q++;
        if (q >= m)
            break;
    }
    System.out.println();
    for (int w = 0; w < a.length; w++)
        System.out.println(a[w]);

}

private static void showExch() {
    // 输入数组，最大的与第一个元素交换，最小的与最后一个元素交换，输出数组。
    int[] a = { -1, -2, 3, 4, 5, 7, 6 };// 7,-1,3,4,6,-2
    int min = a[0], max = a[0];
    int m = 0, n = 0;// 1 5
    for (int i = 0; i < a.length; i++) {
        if (a[i] < min) {
            min = a[i];
            m = i;
        }
        if (a[i] > max) {
            max = a[i];
            n = i;
        }

    }
    System.out.println(max + " " + n + " " + min + " " + m);
    int temp1 = a[0], temp2 = a[a.length - 1];
    a[0] = max;
    a[n] = temp1;
    a[a.length - 1] = min;
    a[m] = temp2;
    for (int j = 0; j < a.length; j++) {
        System.out.println(a[j]);
    }
}

private static void showDiff() {
    // 利用随机数生成一个整数数组，数组中有10个元素，每个元素的值都在1-30之间，且要求各个数值不能相同。打印该数组。
    int[] a = new int[10];
    Set set = new HashSet<>();
    int i = 0;
    while (true) {
        int random = (int) (Math.random() * 10 + 1);
        set.add(random);
        if (set.size() == 10)
            break;
    }
    for (Integer integer : set) {
        a[i] = integer;
        i++;
    }
    for (int j = 0; j < a.length; j++)
        System.out.println(a[j]);
}

private static void showInsert() {
    // 有一个已经排好序的数组。现输入一个数，要求按原来的规律将它插入数组中。
    int[] a = { 1, 2, 3, 4, 6, 7 };
    int[] b = new int[a.length + 1];
    int c = 5;
    b = Arrays.copyOf(a, b.length);
    for (int i = a.length - 1; i >= 0; i--) {
        if (c < b[i])
            b[i + 1] = b[i];
        else {
            b[i + 1] = c;
            break;
        }
    }
    for (int k = 0; k < b.length; k++)
        System.out.print(b[k] + " ");
}

private static void showSum() {
    // 求一个3*3矩阵对角线元素之和
    /**
     * 88 33 167 24 48 191 158 151 61
     */
    int[][] a = new int[3][3];
    int b = 0;
    for (int i = 0; i < a.length; i++) {
        for (int j = 0; j < a[i].length; j++) {
            a[i][j] = (int) ((Math.random() * 9 + 1) * 20);
            System.out.print(a[i][j] + " ");
            if (i == j)
                b += a[i][i];
        }
    }
    System.out.print("\n" + b);
}

private static void showSort() {
    // 对10个整数进行按照从小到大的顺序排序
    int[] a = new int[10];
    for (int i = 0; i < 10; i++) {
        a[i] = (int) ((Math.random() * 9 + 1) * 10000);
        System.out.print(a[i] + " ");
    }
    System.out.println();
    for (int j = 0; j < a.length; j++) {
        for (int k = 0 + j; k < a.length; k++) {
            if (a[j] < a[k]) {
                int temp = a[j];
                a[j] = a[k];
                a[k] = temp;
            }
        }
    }
    for (int m = 0; m < a.length; m++)
        System.out.print(a[m] + " ");
}

private static void showFeb() {
    // 用数组求出斐波那契数列的前20项值
    int[] a = new int[20];
    for (int i = 0; i < 20; i++) {
        if (i == 0 || i == 1) {
            a[i] = i + 1;
        } else {
            a[i] = a[i - 1] + a[i - 2];
        }
        System.out.print(a[i] + " ");
        if (i % 5 == 0)
            System.out.println();
    }

}

private static void showA_Number() {
    /*
     * 创建一个char类型的36个元素的数组，前26个元素放置'A'-'Z', 后10个元素放置'0'-'9'。 使用for循环访问所有元素并打印出来。
     * 提示：char类型数据运算 'A'+1 -> 'B'，'0'+1 -> '1'
     */
    char[] a = new char[36];
    for (int i = 0; i < a.length; i++) {
        if (i < 26)
            a[i] = (char) (i + 65);
        else
            a[i] = (char) (i - 26 + '0');
    }
    for (int j = 0; j < a.length; j++) {
        System.out.print(a[j] + " ");
        if (j % 5 == 0)
            System.out.println();
    }
}

private static void showA_Z() {
    /*
     * 创建一个char类型的26个元素的数组，分别 放置'A'-'Z'。 使用for循环访问所有元素并打印出来。 小提示 A 65,a 97
     */
    char[] a = new char[26];
    for (int i = 0; i < a.length; i++) {
        a[i] = (char) (i + 65);
    }
    for (int j = 0; j < a.length; j++) {
        System.out.print(a[j] + " ");
        if (j % 5 == 0)
            System.out.println();
    }
}

}