Java String concat()

In this tutorial, we will learn about the Java String concat() method with the help of examples.

The concat() method concatenates (joins) two strings and returns it.

Example

class Main {
  public static void main(String[] args) {
    String str1 = "Java";
    String str2 = "Programming";

    // concatenate str1 and str2
System.out.println(str1.concat(str2));
} } // Output: JavaProgramming

Syntax of concat()

The syntax of the string concat() method is:

string.concat(String str)

Here, string is an object of the String class.


concat() Parameters

The concat() method takes a single parameter.

  • str - string to be joined

concat() Return Value

  • returns a string which is the concatenation of string and str (argument string)

Example: Java concat()

class Main {
  public static void main(String[] args) {
    String str1 = "Learn ";
    String str2 = "Java";

    // concatenate str1 and str2
System.out.println(str1.concat(str2)); // "Learn Java"
// concatenate str2 and str11
System.out.println(str2.concat(str1)); // "JavaLearn "
} }

Using + Operator for Concatenation

In Java, you can also use the + operator to concatenate two strings. For example,

class Main {
  public static void main(String[] args) {
    String str1 = "Learn ";
    String str2 = "Java";

    // concatenate str1 and str2
System.out.println(str1 + str2); // "Learn Java"
// concatenate str2 and str11
System.out.println(str2 + str1); // "JavaLearn "
} }

concat() Vs the + Operator for Concatenation

concat() the + Operator
Suppose, str1 is null and str2 is "Java". Then, str1.concat(str2) throws NullPointerException. Suppose, str1 is null and str2 is "Java". Then, str1 + str2 gives "nullJava".
You can only pass a String to the concat() method. If one of the operands is a string and another is a non-string value. The non-string value is internally converted to a string before concatenation. For example, "Java" + 5 gives "Java5".
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