嵌套循环未正确迭代

Question

我有这段代码，其中有两个循环“i”和“j”。

'j' 是内循环变量，它应该在外循环单次运行时运行 999 到 100。

但它随机运行， 假设 i=999

j=912

j=911

j=910

j=909

j-908

j=907

j=906

然后突然内循环退出，从外循环减1并使i=998

然后开始'j'循环

j=908

j=907

j=906

j=905

j=906

j=905

j=904

j=903

j=902

然后退出内循环......

    int product=0;
    mainloop:
    for(int i=999;i>99;i--){
        for(int j=999;j>99;j--){
            boolean flag= doSomething(i*j);
            if(flag){
                product=i*j;
                System.out.println("Digits are: "+i+" and "+j);
                break mainloop;
            }
        }
    }

 public  boolean doSomething(int product){
        String original= Integer.toString(product),reverse="";
        int length = original.length();
        for ( int i = length - 1; i >= 0; i-- )
            reverse = reverse + original.charAt(i);
        return (original.equals(reverse));


    }

为什么会这样？为什么内循环没有完成从 999 到 100 的循环？

编辑：要清楚，'flag' 仅在 j=913 和 i=993 时为真，这是循环不会中断的主要问题，因为 'j' 永远不会来到 913 但它随机生成数字。此外，'break' 不仅会破坏内部循环，还会破坏主循环。

Answer 1

您在内部循环中有一个条件 - if(flag) - 如果为真，则从该循环中断。这就是内循环没有完成的原因。它不会“随机”运行。它的行为取决于doSomething(i*j) 方法调用的结果。

使用一些额外的调试打印和您声称拥有的doSomething 的实现来运行您的代码：

  int product=0;
  mainloop:
  for(int i=999;i>99;i--){
    System.out.print ("\n"+i+":");
    for(int j=999;j>99;j--){
      System.out.print (j+",");
      boolean flag= doSomething(i*j);
      if(flag){
        product=i*j;
        System.out.println("\nDigits are: "+i+" and "+j);
        break mainloop;
      }
    }
  }

  public static boolean doSomething(int k)
  {
      return k == 913*993;
  }

给出预期的输出：

999:999,998,997,996,995,994,993,992,991,990,989,988,987,986,985,984,983,982,981,980,...,120,119,118,117,116,115,114,113,112,111,110,109,108,107,106,105,104,103,102,101,100,
998:999,998,997,996,995,994,993,992,991,990,989,988,987,986,985,984,983,982,981,980,...,120,119,118,117,116,115,114,113,112,111,110,109,108,107,106,105,104,103,102,101,100,
997:999,998,997,996,995,994,993,992,991,990,989,988,987,986,985,984,983,982,981,980,...,120,119,118,117,116,115,114,113,112,111,110,109,108,107,106,105,104,103,102,101,100,
996:999,998,997,996,995,994,993,992,991,990,989,988,987,986,985,984,983,982,981,980,...,120,119,118,117,116,115,114,113,112,111,110,109,108,107,106,105,104,103,102,101,100,
995:999,998,997,996,995,994,993,992,991,990,989,988,987,986,985,984,983,982,981,980,...,120,119,118,117,116,115,114,113,112,111,110,109,108,107,106,105,104,103,102,101,100,
994:999,998,997,996,995,994,993,992,991,990,989,988,987,986,985,984,983,982,981,980,...,120,119,118,117,116,115,114,113,112,111,110,109,108,107,106,105,104,103,102,101,100,
993:999,998,997,996,995,994,993,992,991,990,989,988,987,986,985,984,983,982,981,980,979,978,977,976,975,974,973,972,971,970,969,968,967,966,965,964,963,962,961,960,959,958,957,956,955,954,953,952,951,950,949,948,947,946,945,944,943,942,941,940,939,938,937,936,935,934,933,932,931,930,929,928,927,926,925,924,923,922,921,920,919,918,917,916,915,914,913,
Digits are: 993 and 913

编辑，doSomething 当 i==995 和 j==583 时，您发布的返回 true。那是你打破循环的时候。