Скачать или смотреть How to Fix string.equals(string) Returning false in Java

Discover the solution to the common issue where `string.equals(string)` returns `false` in Java. Learn how to correctly read user input with Scanner to avoid exceptions and create smoother programs.
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This video is based on the question https://stackoverflow.com/q/68057113/ asked by the user 'Mohsen' ( https://stackoverflow.com/u/14378704/ ) and on the answer https://stackoverflow.com/a/68057158/ provided by the user 'Prithvi Raj' ( https://stackoverflow.com/u/6231383/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue: string.equals(string) Turns False in Java

When programming in Java, it's common to encounter situations where your string.equals(string) checks yield unexpected results. This often leads to frustrating bugs in your applications. One such common scenario arises when dealing with user input via the Scanner class while incorporating conditional statements in loops.

In this guide, we’ll dissect a Java program causing an error when attempting to terminate a loop by entering the letter "F". Let’s identify the problem and explore how to fix it.

The Problem

Consider the following snippet of a Java program:

[[See Video to Reveal this Text or Code Snippet]]

The Error Encountered

When you run this program, it operates as expected until you decide to quit the loop by entering "F". Instead of breaking the loop, you observe the following error message:

[[See Video to Reveal this Text or Code Snippet]]

This indicates that while the input "F" was processed, the program tried to parse it as an integer, leading to a NumberFormatException.

Breaking Down the Solution

The source of the problem lies in how the Scanner object is being used in the condition checks. Here’s how to correct the errors effectively.

Understanding the Scanner

To check user input correctly, you need to read the string input using the Scanner class. Here's how it can be done:

[[See Video to Reveal this Text or Code Snippet]]

By reading the input into a string variable, you can easily compare the string input to "f" or "F".

Revised Code

Here’s the corrected version of your program:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Made

Reading Input as a String: By storing the user input into a string variable, you're able to compare it accurately.

Using equalsIgnoreCase: This method allows you to avoid checking both "F" and "f" separately; it simplifies the condition.

Error Handling: Wrapped the integer parsing in a try-catch block to capture possible parsing errors gracefully.

Conclusion

In summary, ensuring you compare strings correctly when using the Scanner class is crucial to prevent unnecessary exceptions in your Java programs. Always read user input as strings before performing any comparisons or parsing operations. With this approach, you'll create programs that are more robust and user-friendly.

Happy coding!