java--用for\while\do...while输出九九乘法

class ForDemo{

public static void main(String[] args){

for(int x = 1;x<=9;x++){

for(int y = 1;y<=x;y++){       //当X=1时，Y=1,满足y<=x,输出为1*1=1\t，然后Y++，y=2,不满足y<=x,退出内循环，输出换行，进入外循环x++

System.out.print(y+"*"+x+"="+y*x+"\t");//x=2，y=1,满足y<=x,输出1*2=2\t,然后y++,y=2,满足y<=x,输出2*2=4\t,然后y++,y=3,不满足

} //y<=x,退出内循环，输出换行，进入外循环.......

System.out.println();

}

}

}

class WhileDemo{

public static void main(String[] args){

int x = 1;

while(x <= 9){

int y = 1;

while(y <= x){

System.out.print(y+"*"+x+"="+y*x+"\t");

y++;

}

x++;

System.out.println();

}

}

}

class DoWhileDemo{

public static void main(String[] args){

int x = 1;

do{

int y = 1;

do{

System.out.print(y+"*"+x+"="+y*x+"\t");

y++;

}while(y<=x);

System.out.println();

x++;

}while(x<=9);

}

}

do...while先执行一次循环体，然后再判断条件，所以至少执行一次。