Java - 抛出和捕获相同的方法

Question

我无法理解现有代码。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，所以我准备了示例。在 Java 中运行下面的代码会输出什么？

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");
     }
 }

它将是1 2 3 或1 2 4 ？

Answer 1

好吧，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，如果您删除 method() 方法中的 catch 子句，它会为您捕获它:

    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(); 
 }

请记住，try-catch 的意思是:CATCH IT OR THROW IT(其他人会捕获它，否则它会转到 main 并停止您的进程)。