Java String Concatenation

In this chapter you will learn:

How to add strings together
How to concatenate String with other data types
How to concatenate one string to the other with concat method

Add strings together

You can use + operator to concatenate strings together. For example, the following fragment concatenates three strings:

public class Main {
  public static void main(String[] argv) {
    String age = "9";
    String s = "He is " + age + " years old.";
    System.out.println(s);//from   java  2  s .  co m
  }
}

The following code uses string concatenation to create a very long string.

public class Main {
  public static void main(String args[]) {
/*from   j a v a  2s .  c o m*/
    String longStr = "A demo 2s.      com" + 
                     "B d e m o 2 s . c o m                     " + 
                     "C demo                 2s.com" + 
                     "D demo2s.com .";

    System.out.println(longStr);
  }
}

Concatenate String with Other Data Types

You can concatenate strings with other types of data.

public class Main {
  public static void main(String[] argv) {
    int age = 1;//  j a v a  2  s.com
    String s = "He is " + age + " years old.";
    System.out.println(s);
  }
}

The output:

Be careful when you mix other types of operations with string concatenation. Consider the following:

public class Main {
  public static void main(String[] argv) {
    String s = "four: " + 2 + 2;
    System.out.println(s);// j  a  v a 2 s  . c  om
  }
}

This fragment displays

rather than the

To complete the integer addition first, you must use parentheses, like this:

String s = "four: " + (2 + 2);

Now s contains the string "four: 4".

concat one string to the other with concat method

String concat(String str) concatenates the specified string to the end of this string.

public class Main {
  public static void main(String[] argv) {
    String str = "demo2s.com";
    //from   j a  va 2s .  c  om
    str = str.concat("Demo2s.com");
    System.out.println(str);
  }
}