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