java 数组2

一、创建异常

1、空指针异常

2、超出索引范围

二、遍历

for循环

三、求数组中的最大值

package cn.wt.day05.demon02;

public class DemonArray03 {
    public static void main(String[] args) {
        int[] array = {10, 2, 3, 7, 9, 8, 3, 4, 20};
        int max = array[0];
        for (int i = 1; i < array.length; i++) {
            if (array[i] > max){
                max = array[i];
            }
        }
        System.out.println(max);

    }
}

四、反转数组的数据

1、方法一，通过另一个数组

package cn.wt.day05.demon02;

public class DemonArray04 {
    public static void main(String[] args) {
        int[] arr1 = {2, 1, 5, 3};
        int[] arr2 = new int[arr1.length];
        for (int i = 0; i < arr1.length; i++) {
            arr2[arr1.length-1-i] = arr1[i];
        }
        for (int i = 0; i < arr2.length; i++) {
            System.out.println(arr2[i]);
        }
    }
}

2、方法二，通过中间值

package cn.wt.day05.demon02;

public class DemonArray05 {
    public static void main(String[] args) {
        int[] arr = {2, 4, 1, 8, 5, 0};
        int temp;
        for (int i = 0; i < (int)arr.length/2; i++) {
            temp = arr[i];
            arr[i] = arr[arr.length-1-i];
            arr[arr.length-1-i] = temp;
        }

        for (int i = 0; i < arr.length; i++) {
            System.out.println(arr[i]);
        }
    }
}

五、数组作为 方法参数

package cn.wt.day05.demon02;

public class DemonArray06 {
    public static void main(String[] args) {
        int[] array = {1, 5, 2, 7, 3, 5, 0};
        printArray(array);
    }

    public static void printArray(int[] arr){
        for (int i = 0; i < arr.length; i++) {
            System.out.println(arr[i]);
        }
    }
}

注意：python中有默认参数陷阱

六、数组 作为返回值

python 通过 tuple 直接返回

package cn.wt.day05.demon02;

public class DemonArray07 {
    public static void main(String[] args) {
        int[] result = isCal(10, 20);
        System.out.println(result[1]);
    }

    public static int[] isCal(int a, int b){
        int isSum = a + b;
        int isMax = a > b ? a:b;
        int isAvg = (a+b)/2;
        int[] total = {isSum, isMax, isAvg};
        return total;
    }
}

总结：

1、数据类型相同，运行过程中长度不可改变

2、参数、返回值 都是内存地址

3、异常：空指针、超出索引范围

4、遍历，最值，反转