在为用户打印代码之前,java是否会创建所有用于递归的堆栈帧?

发布于 2025-01-14 10:46:45 字数 516 浏览 0 评论 0原文

这是一个简单的递归示例,我们从一个数字开始倒数。当单击“运行”时,java是否计算5,4,3,2,1,0,然后将这些数字存储在6个堆栈帧中,然后才打印代码?或者它可能计算 5,将其添加到调用堆栈,4 将其添加到调用堆栈等等......

public static void main(String[] args) {
   countDown(5);
}
public static void countDown(int n){
 if(n <= 0){
     System.out.println(n);
 }
 else{
     System.out.println(n);
     --n;
     countDown(n);

     //Call stack pops 5 times from the 5 calls from here up until the method call
     //Test will print 5 times
     System.out.println("Test");
      }
 }

So here is a simple example of recursion where we count down from a number. When clicking run does java calculate 5,4,3,2,1,0 store those numbers in 6 stack frames only then does it print the code? Or maybe it calculates 5, adds it to call stack, 4 adds it to call stack etc...

public static void main(String[] args) {
   countDown(5);
}
public static void countDown(int n){
 if(n <= 0){
     System.out.println(n);
 }
 else{
     System.out.println(n);
     --n;
     countDown(n);

     //Call stack pops 5 times from the 5 calls from here up until the method call
     //Test will print 5 times
     System.out.println("Test");
      }
 }

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评论(1

三人与歌 2025-01-21 10:46:45

是的,您可以使用 Thread.currentThread().getStackTrace() 方法:

import java.util.Arrays;

class StackFrames {

  public static void main(String[] args) {
     countDown(5);
  }
  public static void countDown(int n){
   if(n <= 0){
       System.out.println(n);
   } else{
       System.out.println(n);
       --n;
       countDown(n);


       //Call stack pops 5 times from the 5 calls from here up until the method call
       //Test will print 5 times
       System.out.println("Test");
       Arrays.stream(
          Thread
          .currentThread()
          .getStackTrace()
      ).forEach(System.out::println);

   }
 }
}

输出:

5
4
3
2
1
0
Test
java.base/java.lang.Thread.getStackTrace(Thread.java:1610)
StackFrames.countDown(StackFrames.java:18)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.main(StackFrames.java:4)
Test
java.base/java.lang.Thread.getStackTrace(Thread.java:1610)
StackFrames.countDown(StackFrames.java:18)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.main(StackFrames.java:4)
Test
java.base/java.lang.Thread.getStackTrace(Thread.java:1610)
StackFrames.countDown(StackFrames.java:18)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.main(StackFrames.java:4)
Test
java.base/java.lang.Thread.getStackTrace(Thread.java:1610)
StackFrames.countDown(StackFrames.java:18)
StackFrames.countDown(StackFrames.java:12)
StackFrames.main(StackFrames.java:4)
Test
java.base/java.lang.Thread.getStackTrace(Thread.java:1610)
StackFrames.countDown(StackFrames.java:18)
StackFrames.main(StackFrames.java:4)

Yes, you can see it for yourself using the Thread.currentThread().getStackTrace() method:

import java.util.Arrays;

class StackFrames {

  public static void main(String[] args) {
     countDown(5);
  }
  public static void countDown(int n){
   if(n <= 0){
       System.out.println(n);
   } else{
       System.out.println(n);
       --n;
       countDown(n);


       //Call stack pops 5 times from the 5 calls from here up until the method call
       //Test will print 5 times
       System.out.println("Test");
       Arrays.stream(
          Thread
          .currentThread()
          .getStackTrace()
      ).forEach(System.out::println);

   }
 }
}

Output:

5
4
3
2
1
0
Test
java.base/java.lang.Thread.getStackTrace(Thread.java:1610)
StackFrames.countDown(StackFrames.java:18)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.main(StackFrames.java:4)
Test
java.base/java.lang.Thread.getStackTrace(Thread.java:1610)
StackFrames.countDown(StackFrames.java:18)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.main(StackFrames.java:4)
Test
java.base/java.lang.Thread.getStackTrace(Thread.java:1610)
StackFrames.countDown(StackFrames.java:18)
StackFrames.countDown(StackFrames.java:12)
StackFrames.countDown(StackFrames.java:12)
StackFrames.main(StackFrames.java:4)
Test
java.base/java.lang.Thread.getStackTrace(Thread.java:1610)
StackFrames.countDown(StackFrames.java:18)
StackFrames.countDown(StackFrames.java:12)
StackFrames.main(StackFrames.java:4)
Test
java.base/java.lang.Thread.getStackTrace(Thread.java:1610)
StackFrames.countDown(StackFrames.java:18)
StackFrames.main(StackFrames.java:4)
~没有更多了~
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