Java String Concatenation

The general meaning of concatenation is a series of interconnected things. String concatenation refers to the combination of more than one string.

Ways of String concatenation:

1. By concatenation operator +.
2. By concat() method.

1. By concatenation operator +

String concatenation can be performed with the + operator. String concatenation is performed by the StringBuilder or StringBuffer class and its append method. The result will be a new string after appending the second string at the end of the first string. Both string and primitive data types can be concatenated.
The compiler will transform it to:

Syntax

String s=(new StringBuilder()).append("firstString").append("secondString").toString();

Example

class TestString{
    String str1 = "www.";
    String str2 = "w3schools.";
    String str3 = "com";
    
    public void concateStrings(){
        System.out.println(str1 + str2 + str3);
    }
}

public class StringConcatenationExample1 {
    public static void main(String args[]){
        //creating TestString object.
        TestString obj = new TestString();
        //method call
        obj.concateStrings();
    }
}

Output

www.w3schools.blog

Note: If any one of the two arguments of the + operator is a string then the result will be a string otherwise primitive type.

class TestString{
    String str1 = "jai";
    int num1 = 10;
    int num2 = 20;
    int num3 = 30;
    int num4 = 40;
    
    public void concateOerations(){
        //As expression executes from left to right and 
        //num1, num2 both are primitive data types will result
        //into primitive, next argument is String and hence
                // will result into a string, next argument num3
                // is a primitive type but as one of the two 
                //operands is a string and hence result will be 
        //a string, same is for num4.		
        System.out.println(num1 + num2 + str1 + num3 + num4);
    }
}

public class StringConcatenationExample2 {
    public static void main(String args[]){
        //creating TestString object.
        TestString obj = new TestString();
        //method call
        obj.concateOerations();
    }
}

Output

30Roy3040

2. By concat() method

This method concatenates the argument string at the end of the current string and returns the resulting string.

Syntax

public String concat(String s)

Example

class TestString{
    String str1 = "www.";
    String str2 = "w3schools.";
    String str3 = "com";
    
    public void concateStrings(){
        System.out.println(str1.concat(str2).concat(str3));
    }
}

public class StringConcatenationExample3 {
    public static void main(String args[]){
        //creating TestString object.
        TestString obj = new TestString();
        //method call
        obj.concateStrings();
    }
}

Output

www.w3schools.blog