使用java二重迴圈列印各種圖案總結：外層迴圈控制行數，是固定的，內層迴圈控制每行的輸出情況，注意寫內層迴圈的滿足條件時，要找到每層輸出的圖形數和外層迴圈的關係，肯定存在一定的關係，要麼是總和一定，要麼是存在某種數學關係。舉幾個例子如下：使用java列印直角三角形、倒直角三角形、等腰三角形、平行四邊形、矩形、實心菱形、四種九九乘法表：

package BiShiTest;

import java.util.Scanner;

import org.junit.Test;
/**
 * 雙重迴圈練習:列印各種圖形和列印四種九九乘法
 * 
 * @author 任志燕 
 * 2017年6月21日
 *
 */
 

public class PrintGraphTest {
    Scanner scanner = new Scanner(System.in);

    //1.列印矩形
    @Test
    public void testOne(){
        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < 4; j++) {
                System.out.print("*");
            }
            System.out.println();
        }
    }

    //2.列印直角三角形
 

    @Test
    public void testTwo(){
        System.out.print("請輸入直角三角形的行數:");
        int row = scanner.nextInt();
        for (int i = 1; i <=row ; i++) {
            for (int j = 1; j <= (2*i-1); j++) {
                System.out.print("*");
            }
            System.out.println();
        }
    }

    //3.列印倒直角三角形
 

    @Test
    public void testThree(){
        System.out.println("請輸入直角三角形的行數:");
        int count = scanner.nextInt();
        for (int i = 1; i <= count; i++) {
            for (int j = 1; j <= count-i+1; j++) {
                System.out.print("*");
            }
            System.out.println();
        }
    }

    //4.1 列印等腰三角形
    @Test
    public void testFour(){
        System.out.println("請輸入等腰三角形的行數:");
        int row = scanner.nextInt();
        for (int i = 1; i <= row; i++) {
            for (int j = 1; j <=(2*row-1); j++) {
                if (j<=row-i) {
                    System.out.print(" ");
                }
                else if (j<(row+i)) {

                    System.out.print("*");
                }
            }
        System.out.println();
        }
    }

    //4.2 列印等腰三角形方法二
    @Test
    public void testFour2(){
        System.out.print("請輸入等腰三角形的行數:");
        int row = scanner.nextInt();
        for (int i = 1; i <= row; i++) {
            //先列印左面空格
            for (int j = 0; j < row-i; j++) {
                System.out.print(" ");
            }
            //列印*
            for (int j = 1; j <= 2*i-1; j++) {
                System.out.print("*");
            }
            System.out.println();
        }
    }


    //5.列印平行四邊形
    @Test
    public void testFive(){
        System.out.print("請輸入平行四邊形的行數:");
        int row = scanner.nextInt();
        for (int i = 0; i < row ; i++) {
            for (int j = 1; j <= 2*row; j++) {
                if (j<=row-i) {
                    System.out.print(" ");
                }else if (j<=2*row-i) {
                    System.out.print("#");

                }
            }
            System.out.println();
        }
    }

    //6.列印菱形
    @Test
    public void testSix(){
        System.out.println("請輸入菱形的行數:");
        int row = scanner.nextInt();
        //正三角
        for (int i = 1; i <=row/2+1; i++) {
            for (int j = 0; j<(row/2+1-i); j++) {
                System.out.print(" ");
            }
            for (int j = 1; j <=2*i-1; j++) {
                System.out.print("*");
            }
            System.out.println();
        }
        //倒三角
        for (int i = row/2; i >=1; i--) {
            for (int j = 1; j<=row/2-i+1; j++) {
                System.out.print(" ");
            }
            for (int j = 1; j <=2*i-1; j++) {
                System.out.print("*");
            }
            System.out.println();
        }
    }




    //7.列印左下角形式的九九乘法表
    @Test
    public void testSeven(){
        for (int i = 1; i <=9 ; i++) {
            for (int j = 1; j <=i; j++) {
                System.out.print(j+"*"+i+"="+(j*i)+"\t");
            }
            System.out.println();
        }
    }

        //8.列印左上三角形式的九九乘法表
        @Test
        public void testEight(){
            for (int i = 9; i >=1 ; i--) {
                for (int j = 1; j <=i; j++) {
                    System.out.print(j+"*"+i+"="+(j*i)+"\t");
                }
                System.out.println();
            }
        }

    //9.列印右上角形式的九九乘法表
    @Test
    public void testNine(){
          for (int i=9; i>=1; i--) {
              for (int j= 9; j>=1; j--) {
                  if (j>i) {
                      System.out.print("\t");
                  }else {
                      System.out.print(i+"*"+j+"="+i*j+"\t");
                  }   
              }
              System.out.println();
             }
        }

        //9.列印右下角形式的九九乘法表
        @Test
        public void testTen(){
          for (int i=1; i<=9; i++) {
              for (int j= 9; j>=1; j--) {
                  if (j>i) {
                      System.out.print("\t");
                  }else {
                      System.out.print(i+"*"+j+"="+i*j+"\t");
                  }   
              }
              System.out.println();
           }
        }

}