java_循环练习和数组练习

ublic class Test02 {
    public static void main(String[] args) {
        for (int i = 100; i < 1000; i++) {
            int bai = i/100%10;
            int shi = i/10%10;
            int ge = i%10;
            
            if (i == bai*bai*bai + shi*shi*shi + ge*ge*ge) {
                System.out.println(i);
            }
        }
    }
}

public class Test04 {
    public static void main(String[] args) {
        char da = 'A';
        char xiao = 'a';
        for (int i = 0; i < 26; i++) {
            System.out.println("大写字母 "+da+" ,小写字母 "+xiao);
            da++; //更新大写字母值
            xiao++; //更新小写字母值
        }
    }
}

    for (int j = 1; j < 10; j++) {
            for (int k = 1; k <= j; k++) {
                System.out.print(k +"*"+ j +"="+ j*k +"\t");
            }
            System.out.println();
        }
    }
}

public class Test01 {
    public static void main(String[] args) {
        int sum = 0;
        for (int i = 0; i < 100; i++) {
            if (i%2==1) {
                sum += i;
            }
        }
        System.out.println("累加和的值 " + sum);
    }
}

class Demo3_Array {
    public static void main(String[] args) {
        int[] arr = {33,77,22,44,55};
        int max = getMax(arr);
        System.out.println(max);
    }

    /*
    获取数组中最大值
    1,返回值类型int
    2,参数列表int[] arr
    */

    public static int getMax(int[] arr) {
        int max = arr[0];
        for (int i = 1;i < arr.length ;i++ ) {            //从数组的第二个元素开始遍历
            if (max < arr[i]) {                            //如果max记录的值小于的数组中的元素
                max = arr[i];                            //max记录住较大的
            }
        }

        return max;
    }
}

public static void printArray(int[] arr) {
    System.out.print("[");
    for (int i = 0; i < arr.length; i++) {
        if (i == arr.length - 1) {
            System.out.println(arr[i]+"]");
        } else {
            System.out.print(arr[i]+", ");
        }
    }
}

//数组元素逆序
public static void receive(int[] arr){
    for (int start = 0, end = arr.length-1; start < end; start++,end--) {
        int temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;
    }
}

public static void selectSort(int[] arr) {
    //功能
    //外层循环用来控制数组循环的圈数
    for (int i = 0; i < arr.length-1; i++) {
        //内层循环用来完成元素值比较，把小的元素值互换到要比较的第一个元素中
        for (int j = i+1; j < arr.length; j++) {
            if (arr[i] > arr[j]) {
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
    }
}

//冒泡排序
public static void bubbleSort(int[] arr) {
    //功能
    //外层循环用来控制数组循环的圈数
    for (int i = 0; i < arr.length-1; i++) {
        //j < arr.length-1 为了避免角标越界
        //j < arr.length-1-i 为了比较效率,避免重复比较
        //内层循环用来完成元素值比较，把大的元素值互换到后面
        for (int j = 0; j < arr.length-1-i; j++) {
            if (arr[j] > arr[j+1]) {
                int temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
            }
        }
    }
}

//二分查找法(折半查找法)
public static int halfSearch(int[] arr, int number) {
    //定义3个变量，用来记录min, min, mid的位置
    int min = 0;
    int max = arr.length-1;
    int mid = 0;
        while (min <= max) {
           mid = (min+max)/2;
        //没找了， 更新范围，继续比较
        //更新范围
        if (arr[mid] > number) {
            //在左边
            max = mid-1;
        } else if(arr[i] < number){
            //在右边
            min = mid+1;
        }
        else{
              return mid ;
          }
     
    return -1;
}

class Test1_Array {
    public static void main(String[] args) {
        int[][] arr = {{1,2,3},{4,5},{6,7,8,9}};

        for (int i = 0;i < arr.length ;i++ ) {            //获取到每个二维数组中的一维数组
            for (int j = 0;j < arr[i].length ;j++ ) {    //获取每个一维数组中的元素
                System.out.print(arr[i][j] + " ");
            }

            System.out.println();
        }
    }
}

class Test2_Array {
    public static void main(String[] args) {
        int[][] arr = {{22,66,44},{77,33,88},{25,45,65},{11,66,99}};

        int sum = 0;                                    //定义变量,记录每次相加的结果
        for (int i = 0;i < arr.length ;i++ ) {            //获取每一个一维数组
            for (int j = 0;j < arr[i].length ;j++ ) {    //获取每一个一维数组中的元素
                sum = sum + arr[i][j];                    //累加
            }
        }

        System.out.println(sum);
    }
}

class Test3_Array {
    public static void main(String[] args) {
        /*int a = 10;
        int b = 20;
        System.out.println("a:"+a+",b:"+b);            //a = 10,b = 20
        change(a,b);
        System.out.println("a:"+a+",b:"+b);            //?*/

        int[] arr = {1,2,3,4,5};
        change(arr);
        System.out.println(arr[1]);
    }

    public static void change(int a,int b) {        //a = 10, b= 20
        System.out.println("a:"+a+",b:"+b);            //a = 10,b = 20
        a = b;                                        //a = 20
        b = a + b;                                    //b = 40
        System.out.println("a:"+a+",b:"+b);            //a = 20, b = 40
    }

    public static void change(int[] arr) {            //1,4,3,8,5
        for(int x=0; x<arr.length; x++) {
            if(arr[x]%2==0) {
                arr[x]*=2;
            }
        }
    }
}