The concat() method in Java is used to append one string to another and returns a new combined string. It does not modify the original string since strings are immutable.
- Used to concatenate (join) two strings
- Returns a new string as the result
- Throws NullPointerException if the argument is null
Java
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);
}
}
Syntax
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:
Example: Combining Two Strings with concat() Method
Java
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);
}
}
Example: Sequential Concatenation of Multiple Strings
java
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);
}
}
OutputComputer-Science-
Computer-Science-Portal
Note: Strings are immutable in Java, so every concatenation creates a new string object instead of modifying the existing one.
Example: Handling NullPointerException in String concat()
Java
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.NullPointerException
Example: Reversing a String Using concat() Method
Java
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);
}
}
