Java - throw and catch in same method

Question

I have problem with understand existing code. I would like to know how Java manage throw exception and catch it in same method. I can't find it in other question so I preapare example. What will be output of run below code in Java?

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");
     }
 }

It will be 1 2 3 or 1 2 4?

Answer 1

Well, let's check:

    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
     }
 }

Now, if you remove your catch clause in the method() method for something like this, now it will catch it for you:

    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(); 
 }

Remember, a try-catch means: CATCH IT OR THROW IT (someone else will catch it, and if not it will go to the main and stop your process).