為什么java中這個遞回函式的結果是這樣的

1. static void h2(int n){
2.        if(n<2)
3.            h2(n 1);
4.        System.out.print(n " ");
5.        if(n<2)
6.            h2(n 1);
7. }

如果我給出這個函式的結果，這個函式是一個遞回函式：有人h2()可以 向我解釋這個函式是如何作業的嗎？ 我還想知道下一個 ==> 例如在呼叫函式時代碼是否繼續到下一行并列印值，或者它繼續并重新開始函式？
n=02 1 2 0 2 1 2

3h2(n 1);n

我添加了一些列印，所以我可以看到發生了什么：

1. static void h2(int n){
2.        int i=0;
3.        if(n<2){
4.            System.out.println("i=" (  i) " first n=" n " ");
5.            h2(n 1);
6.        }
7.        System.out.println("i=" (  i) " n=" n);
8.        if(n<2){
9.            System.out.println("\ni=" (  i) " second n=" n " ");
10.            h2(n 1);
11.       }
12. }

這是這段代碼的輸出：

i=1 first n=0 
i=1 first n=1 
i=1 n=2
i=2 n=1

i=3 second n=1 
i=1 n=2
i=2 n=0

i=3 second n=0 
i=1 first n=1 
i=1 n=2
i=2 n=1

i=3 second n=1 
i=1 n=2

uj5u.com熱心網友回復：

這是一個測驗應用程式，向您顯示程式執行的跟蹤（由于使用 需要 Java 11 String#repeat(int)）：

public class Main {

  private static int depth;

  public static void main(String[] args) {
    foo(0);
  }

  public static void foo(int n) {
    printDebug("Invoked foo("   n   ")");

    if (n < 2) {
      printDebug("Recursively call foo("   n   "   1)");
      depth  ;
      foo(n   1);
      depth--;
      printDebug("Returned from recursive call of foo("   n   "   1)");
    } else {
      printDebug("Skip recursive call");
    }


    // this is the 'System.out.print(n   " "); line'
    printDebug("PRINT VALUE OF n AND A SPACE (n="   n   ")");

    if (n < 2) {
      printDebug("Recursively call foo("   n   "   1)");
      depth  ;
      foo(n   1);
      depth--;
      printDebug("Returned from recursive call of foo("   n    "   1)");
    } else {
      printDebug("Skip recursive call");
    }
  }

  private static void printDebug(String msg) {
    System.out.println("    ".repeat(depth)   msg);
  }
}

遞回函式已重命名foo并稍作修改以適應除錯陳述句。當您運行上述內容時，輸出將是：

Invoked foo(0)
Recursively call foo(0   1)
    Invoked foo(1)
    Recursively call foo(1   1)
        Invoked foo(2)
        Skip recursive call
        PRINT VALUE OF n AND A SPACE (n=2)
        Skip recursive call
    Returned from recursive call of foo(1   1)
    PRINT VALUE OF n AND A SPACE (n=1)
    Recursively call foo(1   1)
        Invoked foo(2)
        Skip recursive call
        PRINT VALUE OF n AND A SPACE (n=2)
        Skip recursive call
    Returned from recursive call of foo(1   1)
Returned from recursive call of foo(0   1)
PRINT VALUE OF n AND A SPACE (n=0)
Recursively call foo(0   1)
    Invoked foo(1)
    Recursively call foo(1   1)
        Invoked foo(2)
        Skip recursive call
        PRINT VALUE OF n AND A SPACE (n=2)
        Skip recursive call
    Returned from recursive call of foo(1   1)
    PRINT VALUE OF n AND A SPACE (n=1)
    Recursively call foo(1   1)
        Invoked foo(2)
        Skip recursive call
        PRINT VALUE OF n AND A SPACE (n=2)
        Skip recursive call
    Returned from recursive call of foo(1   1)
Returned from recursive call of foo(0   1)

每行的縮進顯示遞回呼叫的當前深度（更多縮進意味著更深的遞回）。如果您查看PRINT VALUE OF n AND A SPACE (n=#)行的順序，您會看到原始遞回函式的輸出將是：

2 1 2 0 2 1 2

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