代码：双重for循环打印简单图形

//长方形
for(int i = 0; i < 5; i++){
for(int j = 0; j < 5; j++){
System.out.print("*");
}
System.out.println();
}

*****
*****
*****
*****
*****

//平行四边形
for(int i = 0; i < 5; i++){
for(int j = 0; j < 5-1 - i; j++){
System.out.print(" ");
}
for(int j = 0; j < 5; j++){
System.out.print("*");
}
System.out.println();
}

    *****
*****
*****
*****
*****

//三角形
for(int i = 1; i <= 5; i++){
for(int j = 1; j <= 5 - i; j++){
System.out.print(" ");
}
for(int j = 1; j <= 2*i - 1; j++){
System.out.print("*");
}
System.out.println();
}

*
***
*****
*******
*********

//菱形
for(int i = 1; i <= 5; i++){
for(int j = 1; j <= 5 - i; j++){
System.out.print(" ");
}
for(int j = 1; j <= 2*i - 1; j++){
System.out.print("*");
}
System.out.println();
}
for(int i = 1; i <= 4; i++){
for(int j = 1; j <= i; j++){
System.out.print(" ");
}
for(int j = 1; j <= 2*(5-i)-1; j++){
System.out.print("*");
}
System.out.println();
}

*
***
*****
*******
*********
*******
*****
***
*

//数字菱形
for(int i = 1; i <= 5; i++){
for(int j = 1; j <= 5 - i; j++){
System.out.print(" ");
}
for(int j = 1; j <= 2*i - 1; j++){
System.out.print(5-i);
}
System.out.println();
}
for(int i = 1; i <= 4; i++){
for(int j = 1; j <= i; j++){
System.out.print(" ");
}
for(int j = 1; j <= 2*(5-i)-1; j++){
System.out.print(i);
}
System.out.println();
}

4
333
22222
1111111
000000000
1111111
22222
333
4

//空心菱形
for(int i = 1; i <= 5; i++){
for(int j = 1; j <= 5 - i; j++){
System.out.print(" ");
}
for(int j = 1; j <= 2*i - 1; j++){
if(j == 1 || j == 2*i - 1){
System.out.print("*");
}else{
System.out.print(" ");
}
}
System.out.println();
}
for(int i = 1; i <= 4; i++){
for(int j = 1; j <= i; j++){
System.out.print(" ");
}
for(int j = 1; j <= 2*(5-i)-1; j++){
if(j == 1 || j == 2*(5 - i)-1){
System.out.print("*");
}else{
System.out.print(" ");
}
}
System.out.println();
}

*
* *
*   *
*     *
*       *
*     *
*   *
* *
*

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

1*1=1
2*1=2   2*2=4
3*1=3   3*2=6   3*3=9
4*1=4   4*2=8   4*3=12  4*4=16
5*1=5   5*2=10  5*3=15  5*4=20  5*5=25
6*1=6   6*2=12  6*3=18  6*4=24  6*5=30  6*6=36
7*1=7   7*2=14  7*3=21  7*4=28  7*5=35  7*6=42  7*7=49
8*1=8   8*2=16  8*3=24  8*4=32  8*5=40  8*6=48  8*7=56  8*8=64
9*1=9   9*2=18  9*3=27  9*4=36  9*5=45  9*6=54  9*7=63  9*8=72  9*9=81