Java小白-2.流程控制

• 选择/条件语句:

1. if条件语句

        if{}

        if{}else{}

        if{}else if{}else{}

2.switch

private void switch_demo(int num) {  
    switch (num) {  
    case 1:  
        System.out.println("星期一");  
        break;  
    case 2:  
        System.out.println("星期二");  
        break;  
    case 3:  
        System.out.println("星期三");  
        break;  
    case 4:  
        System.out.println("星期四");  
        break;  
    case 5:  
        System.out.println("星期五");  
        break;  
    case 6:  
        System.out.println("星期六");  
        break;  
    case 7:  
        System.out.println("星期日");  
        break;  
    default:  
        System.out.println("没有对应的星期数");  
        break;  
    }  
}  

​​​​​

• 循环语句

​​​​​​​while

        int a = 1;

        while(a<20){System.out.println(++a);}

do while(先执行,至少循环1次)

        a=1;

        do{System.out.println(++a);} while(a<20);

for

        for(int i=0;i<20;i++) {System.out.println(++i); }

• ​​跳转语句

​​​​​​​break

​​​​​​​        跳出switch,循环(while(true) { if(++a>50) { break;}});跳出代码块block1: { block2: { a++;if(a>5) { break block1;}}}只跳出所在循环外部循环不跳出

continue(继续下一次循环)   

return

-----------

练习:九九乘法表

public class Print99 {  
    public static void main(String[] args) {  
        System.out.println("*******************************九九乘法表********************************");  
  
        for (int i = 1; i <= 9; i++) {  
            System.out.print("\t"+i);  
        }  
          
        System.out.println();  
          
        for (int i = 1; i <= 9; i++) {  
            System.out.print(i+"\t");  
            for (int j = 1; j <= i; j++) {  
                System.out.print(i*j+"\t");  
            }  
            System.out.println();  
        }  
    }  
} 

输出: