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Java String With Example

In this tutorial, we will learn about Java strings, how to create them, and the various methods of the String class.

A string in Java is a sequence of characters. For example, “Java” is a string made up of the characters ‘J’, ‘a’, ‘v’, ‘a’.

In Java, we use double quotes to represent a string. As an example:

// create a string
String Sample = “Developers Dome”;

In this case, we’ve created a string variable called Sample. “Developers Dome” is used to initialize the variable.

Example: In Java, create a String.

class Main {
  public static void main(String[] args) {
    
    // create strings
    String sample = "Kotlin";
    String sample1 = "Ruby";
    String sample2 = "Java";

    // print strings
    System.out.println(sample);   
    System.out.println(sample1);  
    System.out.println(sample2);   
  }
}

Output:

Kotlin
Ruby
Java

In the preceding example, we created three strings marked sample, sample1, and sample2. In this case, we are directly creating strings as primitive types.

Strings are not primitive types in Java (like int, char, etc).  On the other hand, all the strings are objects of a predefined class called String.

How to create a string object?

String objects can be created in two ways:

  1. As a string literal
  2. By using a new keyword

1: String Literal

Double quotes are used to create a Java String literal.

Example:

String sample=”Developers Dome”;  

When you create a string literal, the JVM first checks the “string constant pool.” If the string is already in the pool, a pointer to the pooled instance is returned. If the string does not already exist in the pool, a new string instance is created and added to it.

String literals are used in Java to improve Java’s memory efficiency

2: By new keyword

The literal “DevelopersDome” will be placed in the string constant pool, and JVM will create a new string object in normal (non-pool) heap memory. The variable will be used to refer to a heap object (non-pool).

String sample =new String(“Welcome”);

Example: Java String Example

public class Sample{    
public static void main(String args[]){    
String x="java";//creating string by Java string literal    
char ch[]={'s','t','r','i','n','g'};    
String y=new String(ch);
String z=new String("DevelopersDome");//Java string by new keyword    
System.out.println(x);    
System.out.println(y);    
System.out.println(z);    
}}    

Output:

Java
String
DevelopersDome

Methods of Java String

Aside from the methods mentioned above, Java includes a number of string methods. Here are a few examples of these methods:

MethodsDescription
contains()determines whether or not the string contains a substring
substring()returns the string’s substring
replace()substitutes the specified new character for the specified old character
replaceAll()all substrings that match the regex pattern are replaced
replaceFirst()replace the first substring that matches
charAt()returns the character that can be found in the specified location
getBytes()converts the string to a bytes array
indexOf()The position of the specified character in the string is returned.
compareTo()compares two strings in the order of their appearance in the dictionary
compareToIgnoreCase()compares two strings while disregarding case differences
trim()removes any whitespace at the beginning and end of a sentence
format()returns a formatted string
split()divides a string into an array of strings
toLowerCase()converts the string’s case to lowercase
toUpperCase()converts the string’s case to uppercase
valueOf()The string representation of the specified argument is returned.
toCharArray()transforms a string into a char array
matches()determines if the string matches the regex
startsWith()determines if the string starts with the specified string
endsWith()determines if the string ends with the given string.
isEmpty()determines if a string is empty or not
intern()returns the string’s canonical representation
contentEquals()determines if the string is equal to the charSequence
hashCode()returns the string’s hash code

Strings in Java: immutable

String objects are immutable in Java. Immutable simply means that it cannot be changed or modified. The data or state of a String object can’t be changed once it’s been created, instead, a new String object is created.

  • Consider the following scenario to gain a better understanding:
// Create String
String sample = “DevelopersDome”;

We’ve created a string variable called example in this case. The string ” DevelopersDome” is stored in the variable.

Let’s say we want to modify the string.

// add another string “Hello” to the previous string example
sample = sample .concat(” Hello”);
  • The concat() method is being used to add another string Hello to the previous string.
  • It appears that we have the ability to change the previous string’s value. This, however, is not the case. Let’s take a look at what’s going on here.
  • JVM takes the first string “DevelopesDome” and adds “Hello” to it to make a new string. It then assigns the new string “DevelopersDome Hello” to the sample variable, leaving the first string “DevelopersDome” unchanged.

Escape character: Java Strings

What is escape character?

When a character in Java is preceded by a backslash (), it is referred to as a Java escape sequence or escape characters. It could contain letters, numerals, punctuation marks, and so on. These characters are interpreted by the Java compiler as a single character that gives the compiler a specific meaning.

Let’s say we need to use double quotes within a string.

// include double quote
String sample = “It is a “Hello” class”;
  • Because double quotes are used to represent strings, the compiler will treat “It is a” as a string. As a result, the code above will result in an error.
  • In Java, we use the escape character to solve this problem. As an example:
// using the escape character
String sample = “It is a \”Hello\” class.”;

Java String Operations

Java String has a number of methods for performing various operations on strings. We’ll take a look at some of the most common string operations.

1: Join Two Java Strings

The concat() method in Java can be used to join two strings. As an example:

class Main {
  public static void main(String[] args) {

    //  first string
    String demo1 = "Developers";
    System.out.println("First String: " + demo1);

    // second string
    String demo2 = "Dome";
    System.out.println("Second String: " + demo2);

    // join two strings
    String add = demo1.concat(demo2);
    System.out.println("Add String: " + add);
  }
}

Output:

First String: Developers
Second String: Dome
Add String: DevelopersDome

2. Get length of a String

The length() method of the String is used to determine the length of a string. As an example:

class Main {
  public static void main(String[] args) {

    // create string
    String sample = "Hello World";
    System.out.println("String: " + sample);

    // length of sample
    int length = sample.length();
    System.out.println("Length is: " + length);
  }
}

Output:

String: Hello World
Length: 11

3: Reverse a String

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In this example, we will reverse a string in java:

public class ReverseString {  
public static String reverseString(String str){  
    char ch[]=str.toCharArray();  
    String rev="";  
    for(int i=ch.length-1;i>=0;i--){  
        rev+=ch[i];  
    }  
    return rev;  
}  
}  
public class sample {  
public static void main(String[] args) {  
    System.out.println(ReverseString.reverseString("DevelopersDome"));  
    System.out.println(ReverseString.reverseString("Hello EveryOne"));      
    }  
}  

Output:

emoDsrepoleveD
enOyrevE olleh

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We hope that this article will assist you in understanding all about  Java String. We have concentrated on making a basic, meaningful, and easy-to-learn guide to the concepts. Still, if you have any problems regarding this, please post them in the comment section, we will be glad to assist you.

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