How to Concatenate Two Strings in Java: A Comprehensive Guide

How can I properly concatenate two strings in Java without errors?

public class StackOverflowTest {
    public static void main(String args[]) {
        int theNumber = 42;
        System.out.println("Your number is " + theNumber + "!");
    }
}

String concatenation in Java can be accomplished using the '+' operator or the StringBuilder class for more complex operations. Understanding the syntax and best practices is crucial to prevent errors and improve performance.

public class ConcatenateExample {
    public static void main(String[] args) {
        String name = "Alice";
        String greeting = "Hello, " + name + '!';
        System.out.println(greeting);  // Output: Hello, Alice!

        // Using StringBuilder for efficiency
        StringBuilder sb = new StringBuilder();
        sb.append("Your number is ").append(42).append("!");
        System.out.println(sb.toString()); // Output: Your number is 42!
    }
}

Causes

• Using the wrong concatenation syntax (e.g., using '.' instead of '+').
• Attempting to concatenate objects not suitable for direct concatenation without conversion.

Solutions

• Use the '+' operator for basic string concatenation.
• Utilize the StringBuilder or StringBuffer class for efficient concatenation, especially in loops.

Mistake: Using '.' instead of '+' for string concatenation.

Solution: Always use the '+' operator to concatenate strings in Java.

Mistake: Not converting non-string types (like int) to String before concatenation.

Solution: In Java, use the '+' operator to automatically convert non-strings to String when concatenating.