Lära Exception Propagation | Advanced Exception Handling

When a Java program runs, exceptions can be thrown from deep within a series of method calls.

Definition

Exception propagation is the process by which an exception moves up the call stack until it is either caught by a matching catch block or, if unhandled, causes the program to terminate.

The throws keyword is used in method declarations to indicate that a method might throw one or more checked exceptions. This means the method does not handle the exception itself, but rather passes responsibility for handling it to the methods that call it.

If a method does not catch an exception with a try-catch block, the exception is passed to the method that called it. This continues up the chain of method calls. If none of the methods in the call stack handle the exception, it eventually reaches the Java Virtual Machine (JVM), which will terminate the program and print a stack trace. This mechanism allows you to centralize exception handling at a higher level in your application, rather than handling every possible exception at the point where it might occur.

Main.java


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package com.example;

import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        try {
            readFile();
            System.out.println("File read successfully.");
        } catch (IOException e) {
            System.out.println("Caught exception: " + e.getMessage());
        }
    }

    // This method declares that it throws IOException
    public static void readFile() throws IOException {
        // Simulate an error when reading a file
        throw new IOException("Unable to read file.");
    }
}

In the program above, the readFile method declares that it may throw an IOException using the throws keyword. When readFile is called from main, it does not handle the exception itself. Instead, if an IOException occurs, it is passed up to the main method. The main method contains a try-catch block that catches the IOException and handles it by printing a message.

This demonstrates how the exception travels from the point where it is thrown, through the call stack, until it is eventually caught and handled by a suitable catch block. If the main method did not catch the exception, it would propagate further, and the JVM would terminate the program after printing the stack trace.

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