String in Java

Java String

Java String provides a lot of concepts that can be performed on a string such as compare, concat, equals, split, length, replace, compareTo, intern, substring etc.

In java, string is basically an object that represents sequence of char values.

An array of characters works same as java string. For example:

char[] ch={'j','a','v','a','t','p','o','i','n','t'};  
String s=new String(ch);  
is same as:

String s="javatpoint";  
The java.lang.String class implements Serializable, Comparable and CharSequence interfaces.

The java String is immutable i.e. it cannot be changed but a new instance is created. For mutable class, you can use StringBuffer and StringBuilder class.

We will discuss about immutable string later. Let's first understand what is string in java and how to create the string object.

What is String in java

Generally, string is a sequence of characters. But in java, string is an object that represents a sequence of characters. String class is used to create string object.

How to create String object?

There are two ways to create String object:
By string literal
By new keyword
1) String Literal

Java String literal is created by using double quotes. For Example:

String s="welcome";  
Each time you create a string literal, the JVM checks the string constant pool first. If the string already exists in the pool, a reference to the pooled instance is returned. If string doesn't exist in the pool, a new string instance is created and placed in the pool. For example:

String s1="Welcome";  
String s2="Welcome";//will not create new instance  
java string literal
In the above example only one object will be created. Firstly JVM will not find any string object with the value "Welcome" in string constant pool, so it will create a new object. After that it will find the string with the value "Welcome" in the pool, it will not create new object but will return the reference to the same instance.

Note: String objects are stored in a special memory area known as string constant pool.

Why java uses concept of string literal?

To make Java more memory efficient (because no new objects are created if it exists already in string constant pool).

2) By new keyword

String s=new String("Welcome");//creates two objects and one reference variable  
In such case, JVM will create a new string object in normal(non pool) heap memory and the literal "Welcome" will be placed in the string constant pool. The variable s will refer to the object in heap(non pool).

Java String Example

public class StringExample{  
public static void main(String args[]){  
String s1="java";//creating string by java string literal  
  
char ch[]={'s','t','r','i','n','g','s'};  
String s2=new String(ch);//converting char array to string  
  
String s3=new String("example");//creating java string by new keyword  
  
System.out.println(s1);  
System.out.println(s2);  
System.out.println(s3);  
}}