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String concatenation in java


General meaning of concatenation means a series of interconnected things. String concatenation refers to the combination of more than one string.

Ways of String concatenation:

  1. By concatenation operator +.
  2. By concat() method.

1. By concatenation operator +:

String concatenation can be performed with + operator. String concatenation is performed by StringBuilder or StringBuffer class and its append method. Result will be a new string after appending second string at the end of the first string. Both string and primitive data type can be concatenated.
Compiler will transform it to:
String¬†s=(new¬†StringBuilder()).append(“firstString”).append(“secondString”).toString();

Example:

StringConcatenationExample1.java

/**
 * This program is used to show the concatenation 
 * of strings by + operator.
 * @author codesjava
 */
class TestString{
	String str1 = "www.";
	String str2 = "codesjava.";
	String str3 = "com";
 
	/**
	 * This method is used to concatenate strings using + operator.
	 * @author codesjava
	 */
	public void concateStrings(){
		System.out.println(str1 + str2 + str3);
	}
}
 
public class StringConcatenationExample1 {
	public static void main(String args[]){
		//creating TestString object.
		TestString obj = new TestString();
		//method call
		obj.concateStrings();
	}
}

Output:

www.codesjava.com

Download this example.
Note: If any one of the two arguments of + operator is a string then result will be a string otherwise primitive type.

Example:

StringConcatenationExample2.java

/**
 * This program is used to show the concatenation of 
 * strings and primitive data types by + operator.
 * @author codesjava.
 */
class TestString{
	String str1 = "jai";
	int num1 = 20;
	int num2 = 30;
	int num3 = 40;
	int num4 = 50;
 
	/**
	 * This method is used to concatenate strings and 
	 * primitive data types using + operator.
	 * @author codesjava
	 */
	public void concateOerations(){
		//As expression executes from left to right and 
		//num1, num2 both are primitive data types will result
		//into primitive, next argument is String and hence
                // will result into a string, next argument num3
                // is a primitive type but as one of the two 
                //operands is a string and hence result will be 
		//a string, same is for num4.		
		System.out.println(num1 + num2 + str1 + num3 + num4);
	}
}
 
public class StringConcatenationExample2 {
	public static void main(String args[]){
		//creating TestString object.
		TestString obj = new TestString();
		//method call
		obj.concateOerations();
	}
}

Output:

50jai4050

Download this example.

2. By concat() method:

This method concatenate argument string at the end of current string and return the resulting string.

Syntax: public String concat(String s).

Example:

StringConcatenationExample3.java

/**
 * This program is used to show the concatenation 
 * of strings by concat method.
 * @author codesjava
 */
class TestString{
	String str1 = "www.";
	String str2 = "codesjava.";
	String str3 = "com";
 
	/**
	 * This method is used to concatenate strings using concat method.
	 * @author codesjava
	 */
	public void concateStrings(){
		System.out.println(str1.concat(str2).concat(str3));
	}
}
 
public class StringConcatenationExample3 {
	public static void main(String args[]){
		//creating TestString object.
		TestString obj = new TestString();
		//method call
		obj.concateStrings();
	}
}

Output:

www.codesjava.com

Download this example.
 
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