Java String Manipulation With Example

What is the String?

A string is a sequence of characters.

Example: – “Welcome To My World”

A string is an immutable object which means that value cannot be changed once it is created. If we try to modify the content, it will create a new object.

What is an immutable object?

The class must be declared as final (child classes can’t be created).
Data members in the class must be declared as final (After object creation we can’t change the value) .
The constructor should be parameterized.
All the defined variables should have getter methods.
No setters methods(Not have the opportunity to change the value of the instance variable).

Example for immutable : –


//Point 1: Final class 
public final class UserDetails {
	
	final String userName; // Point 2:final Data members
	final int userId;

	public UserDetails(String userName, int userId) // Point 3 :constructor should be parameterized
	{
		this.userName = userName;
		this.userId = userId;
	}

	// Point 4:All the defined variables should have getter methods
	public String getUserName() {
		return userName;
	}

	public int getUserId() {
		return userId;
	}

	// Point 5: No setters methods

}

class Test {
	public static void main(String args[]) {
		UserDetails userDetails = new UserDetails("Sairam", 568);
		System.out.println("User Name-->" + userDetails.getUserName());
		System.out.println("User Id-->" + userDetails.getUserId());

	}
}

Output :

User Name-->SairamUser Id--> 568

Read : Why string is immutable in java?

How many ways we can create string objects in java?

1.Using String Literals :
Example :
String string1=”Java String”;

The above statement creates a String literal with value “Java String” in the String Constant Pool.

2. Using a new Keyword :
Example :
String string2= new String( “ Java String ”);

The above statement creates a String object in the Heap Memory and String Constant Pool (if not exists in SCP).

3. Using a character array :
Example :
char array[] ={‘s’,’c’,’h’,’o’,’o’,’l’};
String string3= new String( array);

The above statement creates a String object in the Heap Memory and String Constant Pool (if not exists in SCP) .

Example : –

public class StringExample{
	
	public static void main(String[] args) throws Exception {

		String name = "Java String";
		String name2 = new String("Java String");

		if(name==name2) {
			System.out.println("Output-->true");
		}else {
			System.out.println("Output-->false");
		}
		
	}

Output :

Output–>false

How many String objects got created in above snippet?

Two objects will be created.

String name = “Java String”: – This line will create one object in SCP.

String name2 = new String(“Java String”):- This line will create one object in Heap because in SCP already created a reference with “Java String” value, so it will take that reference.