This post demonstrates :

– Different way of concatenating strings in Java.
– concatenate strings using + operator
– concatenate string using String concat() function
– joining strings using StringBuffer/StringBuilder append() method
– joining Strings using join() method added in JDK 8

 

Method 1 : Using + operator

 
+ operator can be used to concatenate string.
 
Example :
 

    String str1 = "Hello";
    String str2 = "World";
                String str3 = str1 +" " + str2;

 

The + operator is overloaded. It can add numbers and concatenate strings.

So, here are the rules to keep in mind while using + operator for concatenation:
 
1. If both operands are numeric, + means numeric addition.
 
2. If either operand is a String, + means concatenation.
 
3. The expression is evaluated left to right.
 

Method 2 : Using String concat() function

 
String class provides a concat() function that can be used for String concatenation.
 
Example :
 

                String str4 = str1.concat(" ").concat(str2);

 

Method 3 : Using StringBuffer or StringBuilder

 

StringBuffer and StringBuffer classes have an append() method that can be used to concatenate strings.
 

    StringBuilder builder = new StringBuilder();
    builder.append(str1).append(" ").append(str2);

 
 

Method 4 : Using String join() method

 

JDK 8 added a new join() method in String class that can be used to concatenate two or more strings.

Along with the strings to join, it also takes a delimiter that it should add between the strings in result.
 

                String joinedString = String.join(" ", str1, str2);
    System.out.println(joinedString);

 
 

Example program with all the above options

 

package com.topjavatutorial;

public class ProgramStringConcatenation {

  public static void main(String[] args) {

    // This program shows multiple ways of concatenating string in java

    String str1 = "Hello";
    String str2 = "World";
    
    //Method 1 : Using + operator
    
    String str3 = str1 +" " + str2;
    
    System.out.println(str3);
    
    
    //Method 2 : Using concat() method
    
    String str4 = str1.concat(" ").concat(str2);
    
    System.out.println(str4);
    
    
    //Method 3 : Using StringBuffer or StringBuilder
    
    StringBuilder builder = new StringBuilder();
    builder.append(str1).append(" ").append(str2);
    
    System.out.println(builder.toString());
    
    //Method 4 : Using join() method added in JDK 8
    
    String joinedString = String.join(" ", str1, str2);
    System.out.println(joinedString);
  }

}

 
Output :
 
Hello World
Hello World
Hello World
Hello World
 

You may also like the following articles:
 
Performance comparison of different methods of Spring concatenation
 
 

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