Java String Concatenation: Methods and Examples

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Question :

Introduce Java String Concatenation and give examples

Réponse :

Java String concatenation is the process of joining two or more strings together to form a single string. In Java, this can be accomplished using the + operator or the concat() method of the String class. Additionally, Java provides the StringBuilder and StringBuffer classes for more efficient string manipulation, especially when concatenating multiple strings in a loop.

Using the + Operator

The simplest way to concatenate strings in Java is by using the + operator. Here are some examples:

public class StringConcatenationExample {
    public static void main(String[] args) {
        String str1 = "Hello";
        String str2 = "World";
        
        // Using + operator
        String result = str1 + " " + str2; // "Hello World"
        System.out.println(result);
    }
}

Using the concat() Method

The concat() method can also be used to concatenate strings. It is a method of the String class.

public class StringConcatMethodExample {
    public static void main(String[] args) {
        String str1 = "Hello";
        String str2 = "World";
        
        // Using concat() method
        String result = str1.concat(" ").concat(str2); // "Hello World"
        System.out.println(result);
    }
}

Using StringBuilder

For more complex concatenation, especially in loops, StringBuilder is preferred due to its efficiency. It is mutable, meaning it can be changed without creating new objects.

public class StringBuilderExample {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        
        sb.append("Hello");
        sb.append(" ");
        sb.append("World");
        
        String result = sb.toString(); // "Hello World"
        System.out.println(result);
    }
}

Using StringBuffer

StringBuffer is similar to StringBuilder, but it is synchronized, making it thread-safe. It is generally used in multi-threaded environments.

public class StringBufferExample {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer();
        
        sb.append("Hello");
        sb.append(" ");
        sb.append("World");
        
        String result = sb.toString(); // "Hello World"
        System.out.println(result);
    }
}

Summary

  • + Operator: Simple and easy to use for concatenating a few strings.
  • concat() Method: Another way to concatenate strings, but less commonly used than the + operator.
  • StringBuilder: Efficient for concatenating strings in loops or when building strings dynamically.
  • StringBuffer: Similar to StringBuilder, but thread-safe.

Choosing the right method for string concatenation depends on the specific use case, especially regarding performance and thread safety.

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