==多维数组练习：==

image

package day07;
public class ArrayTest {
    public static void main(String[] args) {
        int[][] arr = new int[][] {{3,5,8},{12,9},{7,0,6,4}};
    
        int sum = 0;
        for(int i = 0;i < arr.length;i++) {
            for(int j = 0;j < arr[i].length;j++) {
                sum += arr[i][j];
            }
        }
    System.out.println("sum=" + sum);

    }
}

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int[] x,y[];
==
int[] x;
int[] y[]; 

自动类型转换、强制类型提升

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package day07;

public class YangHuiTest1 {
    public static void main(String[] args) {
        //1.声明并初始化数组
        int[][] yangHui = new int[10][];
        //2.给数组的元素赋值
        for(int i = 0;i < yangHui.length;i++) {
            yangHui[i] = new int[i + 1];
            
            //2.1给首末元素赋值
            yangHui[i][0] = yangHui[i][i] = 1;
            //2.2给非首末元素赋值
            if(i > 1) {
                for(int j = 1;j < yangHui[i].length - 1; j++) {
                    yangHui[i][j] = yangHui[i - 1][j - 1] + yangHui[i - 1][j]; 
                }
            }
            
        }
        
        //3.遍历二维数组
        for(int i = 0;i < yangHui.length;i++) {
            for(int j = 0;j <yangHui[i].length;j++) {
                System.out.print(yangHui[i][j]);
            }
            System.out.println();
        }
    }
}