Java String concat() Method with Examples
The string concat() method concatenates (appends) a string to the end of another string. It returns the combined string. It is used for string concatenation in Java. It returns NullPointerException if any one of the strings is Null.
In this article, we will learn how to concatenate two strings in Java.
Program to Concatenate Two Strings using concat() Method in Java
Below is the simplest method to concatenate the string in Java. We will be using the concat() method of String class to append one string to the end of another and return the new string.
// Java Program to Illustrate concat() method of String.
class GFG {
public static void main(String args[]) {
// String Initialization
String s = "Geeks";
// Use concat() method for string concatenation
s = s.concat("forGeeks");
System.out.println(s);
}
}
Output
GeeksforGeeks
Table of Content
Syntax of concat() Method
public String concat (String s);
Parameters:
- A string to be concatenated at the end of the other string.
Return Value:
- Concatenated(combined) string.
Exception:
- NullPointerException: When either of the string is Null.
Java String concat() Examples
There are many ways to use the concat() method in Java:
Sequential Concatenation of Multiple Strings
The below example shows sequential concatenation using String concat() method in Java.
Example:
// Java program to Illustrate Working of concat() method
// in strings where we are sequentially
// adding multiple strings as we need
public class GFG {
public static void main(String args[])
{
String s1 = "Computer-";
String s2 = "Science-";
// Combining above strings by
// passing one string as an argument
String s3 = s1.concat(s2);
// Print and display temporary combined string
System.out.println(s3);
String s4 = "Portal";
String s5 = s3.concat(s4);
System.out.println(s5);
}
}
Output
Computer-Science- Computer-Science-Portal
Note: As perceived from the code we can do as many times as we want to concatenate strings bypassing older strings with new strings to be contaminated as a parameter and storing the resultant string in String datatype.
Handling NullPointerException in String concat()
The below example shows the NullPointerException in String concat() method.
Example:
// Java program to Illustrate NullPointerException
public class GFG {
public static void main(String args[])
{
String s1 = "Computer-";
String s2 = null;
// Combining above strings by
// passing one string as an argument
String s3 = s1.concat(s2);
// It will raise NullPointerException
System.out.println(s3);
}
}
Output:
Exception in thread "main" java.lang.NullPointerExceptionCombining Two Strings with concat() Method
The below example combines two strings using concat() method of string class.
Example:
// Java Program to combine two strings with concat()
class GFG {
public static void main(String args[]) {
// String Initialization
String s1 = "Geeksfor";
String s2 = "Geeks";
// Concatenate the strings s1 and s2 using the concat() method
// and store the result back in s1.
s1 = s1.concat(s2);
System.out.println(s1);
}
}
Output
GeeksforGeeks
Reversing a String Using concat() Method
We can reverse a string using the concat() method of string class. Below is the example to reverse a string in Java.
Example:
// Java Program to reverse a string using concat() method
public class ReverseString {
public static void main(String[] args) {
// Declare original string variable
String a = "Geeks";
// Declare another string variable
// and initialize it with an empty string
String b = "";
// Iterate through each character in string "a"
// from the last index to the first.
for (int i = a.length() - 1; i >= 0; i--) {
// Extract the current character at index "i" of the "a" string
char ch = a.charAt(i);
// Convert the character to a String object
// using the "Character.toString" method
String ch1 = Character.toString(ch);
// Concatenate the converted character String
// to the end of the "b" string
b = b.concat(ch1);
}
System.out.println("" + a);
System.out.println("" + b);
}
}
Output
Geeks skeeG
