String class in java ~ Eploun

String class

The string is an object that represents the sequence of characters.

An array of characters works the same as a java string.

String class available in java.lang.String class package.

Strings are immutable means can't be changed once created.

Even if you try to change then it automatically creates a new Instance.

String references are used to store values exa. username, password.

Immutable means were unmodifiable or unchangeable.

String object state or data can't change but a new object is created.

String class provides some methods to perform operations on strings like euqals(), compare(), concat(), length() etc.

String class implements three interfaces Serializable, Comparable, and CharSequence.

For example:

char[] ch={'l','e','a','r','n','j','a','v','a'};

String s=new String(ch);

Equal to

String s="learnjava";

Example

public class Demo{

public static void main(String args[]){

String s1="java"; //creating string by string literal

char ch[]={'s', 't', 'r' ,'i', 'n', 'g', 's'}; // character array

String s2=new String(ch); //converting char array to string

String s3=new String("Hello"); //creating Java string by new keyword

System.out.println(s1);

System.out.println(s2);

System.out.println(s3);

}

Output

java

strings

Hello

When creating a String object using the new() operator, it always creates a new object in heap memory. If we create an object using String literal syntax. It may return an existing object from the String pool if it already exists.

Ways of creating String object.

By string literal
By new keyword

String Literal

The String literal is created by using double quotes.

For Example:

String str="hello";

Every 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 the string doesn't exist in pool, a new string instance is created and kept in the pool.

Example

String s1="hello";

String s2="hello"; // s2 will not create new instance.

For better understanding see the following diagram explanation.

By new keyword

String str=new String ("hello"); //creates two objects and one reference variable

In this case, JVM will create a new string object in normal (non-pool) heap memory, and the literal "hello" will be placed in the string constant pool.

The variable str will refer to the object in a heap (non-pool).

Use of String literal?

To use Java more memory efficiently.

Use Cases

String s1="hello";

String s2="hello";

System.out.print(s1.hashCode()==s2.hashCode()); //true

System.out.print(s1==s2); //true

System.out.print(s1.equals(s2));                                       //true

String s3=new String("hello");
String s4=new String("hello");

System.out.print(s3.hashCode()==s4.hashCode());      //true
System.out.print(s3==s4);                                          //false
System.out.print(s3.equals(s4));                                    //true

I hope this article is helpful for you to understand better way what is a string, and the difference between a string literal and a new operator. Thank you. Be in touch.

About Admin

Hi! I'm Dipak . I'm a Java Developer. Currently pursuing Master's Degree in computer science .I am very curious and eager to explore new technologies. My career objective is to secure a challenging career reputable organization to improve my knowledge, and skills.Expertise in Core Java concepts such as OOPs, Collections, Exception Handling, Lambda Expressions, Stream API etc.Hands-on Experience in frameworks like Spring.Having good experience in developing Rest services using Spring.Hands-on experience in using version control system: GitHubproficient in JAVA.Passionate about implementing and launching new projects.Looking to start my career as an entry-level software engineer with a reputed firm driven by technology.

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