Java-以相同的方法抛出并捕获

Question

我在理解现有代码时遇到问题。我想知道Java如何管理抛出异常并以相同的方法捕获它。我在其他问题中找不到它，所以我先举例子。用Java运行以下代码将输出什么？

public static void main(String [ ] args) {
     try{
         System.out.println("1");
         method();
     }
     catch(IOException e) {
         System.out.println("4");
     }
}

public static void method() throws IOException {
     try {
         System.out.println("2");
         throw new IOException();
     }
     catch(IOException e) {
         System.out.println("3");
     }
 }

将是1 2 3还是1 2 4？

Answer 1

好，让我们检查一下：

    public static void main(String [ ] args) {
         try{
             System.out.println("1"); //<--When your code runs it first prints 1
             method();  //<--Then it will call your method here
         }
         catch(IOException e) { //<---Won't catch anything because you caught it already
             System.out.println("4");
         }
    }

public static void method() throws IOException { //<--Your Signature contains a throws IOException (it could throw it or not)
     try {
         System.out.println("2");  //<--It will print 2 and thow an IOException
         throw new IOException(); //<--now it throws it but as you're using a try catch it will catch it in this method
     }
     catch(IOException e) {//the exception is caught here and it so it will print 3
         System.out.println("3"); //<--Prints 3
     }
 }

现在，如果您在catch方法中删除了method()子句，诸如此类，现在它将为您捕获它：

    public static void main(String [ ] args) {
         try{
             System.out.println("1"); //<--When your code runs it first prints 1
             method();  //<--Then it will call your method here
         }
         catch(IOException e) { //<---It will catch the Exception and print 4
             System.out.println("4");
         }
    }

public static void method() throws IOException { //<--Your Signature contains a trows IOException (it could trhow it or not)
         System.out.println("2");  //<--It will print 2 and thows an IOException
         throw new IOException(); 
 }

[记住，尝试捕获意味着：捕获或抛出它（其他人将捕获它，如果没有捕获，它将进入主要位置并停止您的过程）。

Answer 2

1 2 3将作为输出。

不是4，因为异常被捕获在method的try-catch块中