Java String replace() Method

The replace() method in Java is used to replace characters or substrings within a string. It is a method of the String class and allows you to replace one or more occurrences of a specified character or substring with another character or substring.

The replace( ) method has two forms. The first replaces all occurrences of one character in the invoking string with another character.

Syntax 1:


replace(char oldChar, char newChar)

Note: Replaces all occurrences of the specified oldChar with the newChar in the string.

Syntax 2:


replace(CharSequence oldSubstring, CharSequence newSubstring)

Note: Replaces all occurrences of the specified oldSubstring with the newSubstring in the string.

Return Value: The method returns a new String with the specified replacements made. The original string is not modified, as strings in Java are immutable.

Example:


public class ReplaceExample {
    public static void main(String[] args) {
        String str = "Hello World";
        
        // Replace 'l' with '1'
        String result = str.replace('l', '1');
        
        // Print the resulting string
        System.out.println(result);
    }
}

Output:

He11o Wor1d

In this example, every occurrence of the character ‘l’ is replaced with ‘1’.

Replacing a substring with another substring


public class ReplaceExample {
    public static void main(String[] args) {
        String str = "Hello World";
        
        // Replace "World" with "Friends"
        String result = str.replace("World", "Friends");
        
        // Print the resulting string
        System.out.println(result);
    }
}

Output:

Hello Friends

Replace Multiple Occurrences of a Substring

You can replace all occurrences of a substring with another substring.


public class ReplaceExample {
    public static void main(String[] args) {
        String str = "Potato, Tomato, Cauliflower, Cabbage, Potato";
        
        // Replace all occurrences of "Potato" with "Onion"
        String result = str.replace("Potato", "Onion");
        
        // Print the resulting string
        System.out.println(result);
    }
}

Output:

Onion, Tomato, Cauliflower, Cabbage, Onion

Replace String with No Matches

If the character or substring to be replaced is not found in the string, the original string is returned unchanged.


public class ReplaceExample {
    public static void main(String[] args) {
        String str = "Hello World";
        
        // Try to replace "abc" with "def", which does not exist in the string
        String result = str.replace("abc", "def");
        
        // Print the resulting string (unchanged)
        System.out.println(result);
    }
}

Output:

Hello World