Java String

String is a collection of characters. In Java, string is an class object. A Java string is not a character array and is not terminated by NULL character.

Syntax: In Java, String can be declared as follows:

String s = new String("Java Programming");

String s;
s = new String("Java Programming");

String s = "Java Programming";

Example 1: Write a program in java to input name and display it with hello.

import java.util.Scanner;
class Hello {
    public static void main(String[] args) {
        String s;
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter Name: ");
        s = scan.nextLine();
        System.out.println("Hello, " + s);
        scan.close();
    }
}

Output:

Enter Name: Ankit
Hello, Ankit

Java String methods

The Java String class defines a number of methods that allow us to manipulate a string.

Method	Syntax	Description
length()	s1.length();	Returns the length of string 's1' as integer value.
toLowerCase()	s2=s1.toLowerCase();	Convert characters of s1 in lower case and stored in s2.
toUpperCase()	s2=s1.toUpperCase();	Convert characters of s1 in upper case and stored in s2.
concat()	s1.concat(s2);	Append contents of s2 in s1.
replace()	s2=s1.replace('x', 'y');	It replaces all 'x' in string s1 with 'y' and store in s2. It replaces all occurrence of characters, only not the string.
replaceFirst()	s1=s1.replaceFirst("a", "A");	Replace only the first occurence of character.
trim()	s2=s1.trim();	It removes all the spaces from the beginning and from the end of the string s1 and stored in s2.
equals()	s1.equals(s2);	Compare 2 strings and return true if both the strings are equal otherwise returns false.
equalsIgnoreCase()	s1.equalsIgnoreCase(s2);	Compare 2 strings, but it will ignore the cases.
compareTo()	i=s1.compareTo(s2);	Compare 2 strings and return integer value Returns 0, if both strings are equal, Returns positive number, if s1>s2, and Returns negative number, if s1<s2.
compareToIgnoreCase()	i=s1.compareToIgnoreCase(s2);	Same as compareTo method, except it ignore cases.
substring()	s2=s1.substring(0,4);	Return a part from the string.
charAt()	ch=s1.charAt(5);	Returns the character at specified position.
setCharAt()	s1.setCharAt(n,'x');	It append character in nth position with a character x. Its return type is void.
startsWith()	a.startsWith("hello");
endsWith()	a.endsWith("ld");

In the above table, Data type of s1 and s2 is string, Data type of i and n is int, Data type of ch is character.

Example 1: Java Length() method

import java.util.Scanner;
class Length {
    public static void main(String[] args) {
        String s;
        int len;
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter String: ");
        s = scan.nextLine();
        len = s.length();
        System.out.println("Length = " + len);
        scan.close();
    }
}

Output:

Enter String: Java is Fun
Length = 11

Example 2: Java toLowerCase() method

import java.util.Scanner;
class Lower {
    public static void main(String[] args) {
        String s1;
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter string: ");
        s1 = sc.nextLine();
        s1=s1.toLowerCase();
        System.out.println("String in lowercase = " + s1);
        sc.close();
    }
}

Output:

Enter string: Java is a Coffee
String in lowercase = java is a coffee

Example 3: Java toUpperCase() method

import java.util.Scanner;
class Upper {
    public static void main(String[] args) {
        String s1;
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter string: ");
        s1 = sc.nextLine();
        s1=s1.toUpperCase();
        System.out.println("String in uppercase = " + s1);
        sc.close();
    }
}

Output:

Enter string: Java is a Coffee
String in uppercase = JAVA IS A COFFEE

Example 4: Java concat() method

import java.util.Scanner;
class Concat {
    public static void main(String[] args) {
        String s1, s2, s3;
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter first strings: ");
        s1 = sc.nextLine();
        System.out.print("Enter second strings: ");
        s2 = sc.nextLine();
        s3 = s1 + " " + s2;
        System.out.println("After concat new string is : " + s3);
        sc.close();
    }
}

Output:

Enter first strings: java is
Enter second strings: everywhere
After concat new string is : java is everywhere

Example 5: Java replace() method

import java.util.Scanner;
class Replace {
    public static void main(String[] args) {
        String s1;
        Scanner in = new Scanner(System.in);
        System.out.print("Enter string: ");
        s1 = in.nextLine();
        s1=s1.replace('a', 'A');
        System.out.println("After replace string is: " + s1);
        in.close();
    }
}

Output:

Enter string: java programming
After replace string is: jAvA progrAmming

//It replaces all 'a' character with capital 'A'

Replace String using replace() method

String s1 = learn oops concepts in cpp;
s1=s1.replace("cpp", "java"); // replace cpp with java
System.out.println("After replace string is: " + s1);

Output:

After replace string is: learn oops concepts in java

Example 6: Java replaceFirst() method. Replace only the first occurrence of character

String s1 = java programming;
s1=s1.replaceFirst("a", "A");  //only first occurrence is replaced
System.out.println("After replace string is: " + s1);

Output:

After replace string is: jAva programming

Example 7: Java trim() method

import java.util.Scanner;
class Trim {
    public static void main(String[] args) {
        String s1, s2, s3;
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter string: ");
        s1 = sc.nextLine();
        System.out.print("Enter another string: ");
        s2 = sc.nextLine();
        System.out.println("Before trim: " +s1 + s2);
        s3=s1.trim() + s2.trim();
        System.out.print("After trim: " +s3);
        sc.close();
    }
}

Output:

Enter string:.......Never.......Stop.......
Enter another string:.......Learning.......
Before trim:
.......Never.......Stop..............Learning.......
After trim: Never.......StopLearning
(Here ...(dot) represents spacing)

Example 8: Java equals() method

import java.util.Scanner;
class Equals {
    public static void main(String[] args) {
        String s1, s2;
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter 1st string: ");
        s1 = sc.nextLine();
        System.out.print("Enter 2nd string: ");
        s2 = sc.nextLine();
        boolean a = s1.equals(s2);
        if(a)
            System.out.println("Strings are equal");
        else
            System.out.println("Strings are not equal");
        sc.close();
    }
}

Output:

Enter 1st string: delhi
Enter 2nd string: DELHI
Strings are not equal

Example 9: Java equalsIgnoreCase() method

String s1 = 'delhi';
String s2 = 'DELHI';
boolean a = s1.equalsIgnoreCase(s2);
if(a)
    System.out.println("Strings are equal");
else
    System.out.println("Strings are not equal");

Output:

Strings are equal

Example 10: Java compareTo() method

import java.util.Scanner;
class Compare {
    public static void main(String[] args) {
        String s1, s2;
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter 1st string: ");
        s1 = sc.nextLine();
        System.out.print("Enter 2nd string: ");
        s2 = sc.nextLine();
        int i = s1.compareTo(s2);
        if(i==0)
            System.out.println("Strings are equal");
        else
            if(i<0)
                System.out.println("2nd Strings is greater");
            else
                System.out.println("1st Strings is greater");
        sc.close();
    }
}

Output:

Enter 1st string: delhi
Enter 2nd string: DELHI
Strings are not equal

Example 11: Java compareToIgnoreCase() method

String s1 = 'delhi';
String s2 = 'DELHI';
int i = s1.compareToIgnoreCase(s2);
if(i==0)
    System.out.println("Strings are equal");
else
    if(i<0)
        System.out.println("2nd Strings is greater");
    else
        System.out.println("1st Strings is greater");

Output:

Strings are equal

Example 12: Java substring()

import java.util.Scanner;
class Substring {
    public static void main(String[] args) {
        String s1, s2;
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter string: ");
        s1 = sc.nextLine();
        s2 = s1.substring(0,4);
        System.out.println("Substring is = " + s2);
        sc.close();
    }
}

Output:

Java is my favourite language
Substring is = Java

String s1 = 'New Delhi';
String s2 = s1.substring(3);
System.out.println("Substring is = " + s2);

Output:

New

Example 13: Java charAt()

import java.util.Scanner;
class CharAt {
    public static void main(String[] args) {
        String s1;
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter string: ");
        s1 = sc.nextLine();
        char ch = s1.charAt(5);
        System.out.println("Character at 5th position = " + ch);
        sc.close();
    }
}

Output:

Enter string: Programming
Character at 5th position = a