Java String

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

Syntax: In Java, String is declared as follows:

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

Example 1: Input string name and display with hello.

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

Java String methods

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

S.No.	Method	Syntax	Description
	length()	S1.length()	Return 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 replace all 'x' in string S1 with 'y' and store in S2. It replaces all occurrence of a character with only a character not with the string.
	trim()	S2 = S1.trim()	It remove all the spaces from the beginning and from the end of string s1 and stored in S2.
	equals()	S1.equals(S2)	Compare 2 strings and return true if both the string equal otherwise false.
	equalsIgnoreCase()	S1.equalsIgnoreCase (S2)	It will ignore the cases while comparing the two strings.
	compareTo()	S1.compareTo(S2)	Return negative no if S1<S2, Return Positive number if S1>S2, and return 0 if S1 is equal to S2.
	substring()
	charAt()
	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")

Example: toLowerCase()

public static void main(String[] args) {
    String s1;
    Scanner in = new Scanner(System.in);
    System.out.println("Enter string");
    s1 = in.nextLine();
    s1=s1.toLowerCase();
    System.out.println("S1 = " + s1);
}

Example: toUpperCase()

public static void main(String[] args) {
    String s1;
    Scanner in = new Scanner(System.in);
    System.out.println("Enter string");
    s1 = in.nextLine();
    s1=s1.toUpperCase();
    System.out.println("S1 = " + s1);
}

Example: concat()

public static void main(String[] args) {
    String s1, s2, s3;
    Scanner in = new Scanner(System.in);
    System.out.println("Enter 2 string");
    s1 = in.nextLine();
    s2 = in.nextLine();
    s3 = s1 + s2;
    System.out.println("After concat new string is : " + s3);
}

Example: replace()

public static void main(String[] args) {
	String s1;
	Scanner in = new Scanner(System.in);
	System.out.println("Enter string");
	s1 = in.nextLine();
	//s1=s1.replace('a', 'b');
	//s1=s1.replace("java", "cpp");
	s1=s1.replaceFirst("java", "cpp");
	System.out.println("S1 = " + s1);
}

Example: trim()

Example: equals()

public static void main(String[] args) {
	String s1, s2;
	Scanner in = new Scanner(System.in);
	System.out.println("Enter 1st string");
	s1 = in.nextLine();
	System.out.println("Enter 2nd string");
	s2 = in.nextLine();
	
	//boolean a = s1.equals(s2);
	boolean a = s1.equalsIgnoreCase(s2);
	if(a)
		System.out.println("Strings are equal");
	else
	   System.out.println("Strings are not equal");
}

Example: compareTo()

public static void main(String[] args) {
	String s1, s2;
	Scanner in = new Scanner(System.in);
	System.out.println("Enter 1st string");
	s1 = in.nextLine();
	System.out.println("Enter 2nd string");
	s2 = in.nextLine();
	
	int i = s1.compareTo(s2);
	//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");
}

Example: substring()

public static void main(String[] args) {
	String s1, s2;
	Scanner in = new Scanner(System.in);
	System.out.println("Enter string: ");
	s1 = in.nextLine();
	
	//s2 = s1.substring(3);
	s2 = s1.substring(3,5);
	
	System.out.println("After substring, new string is = " + s2);
}

Example: charAt()

public static void main(String[] args) {
	String s1, s2;
	Scanner in = new Scanner(System.in);
	System.out.println("Enter string");
	s1 = in.nextLine();
	char ch = s1.charAt(5);
	System.out.println("character at 5th position = " + ch);
}

In Java, strings are class objects and implemented using two classes, i.e. String and StringBuffer.