Java String

A string is a group of characters surrounded by double quotes (“ ”).
In Java, a string is an object of the String class, that represents a sequence of characters.

Ways to create String object are: -

By string literal
By new keyword

1. By string literal: - It uses double quotes (“ ”) to create a string.

Example:

String s = “QuipoHouse”;

2.By new keyword: - It uses the “new” keyword to create a string.

Example:

String s = new String(“QuipoHouse”);

Example:

package quipohouse;
public class Java_String
{
	public static void main(String []args)
	{
		String s = “Hi”;
		char c = {‘Q’,’u’,’i’,’p’,’o’,’H’,’o’,’u’,’s’,’e’};
		String s1 = new String(c);
		String s2 = new String(“Team”);
		System.out.println(s);
		System.out.println(s1);
		System.out.println(s2);
	}
}

Output:

Hi
QuipoHouse
Team

String Methods: - Some methods that are supported in the characters string class are :

S.No.	Method	Working
1	Char charAt(int Index)	Return character at specified index
2	boolean isEmpty()	Check if string is empty
3	String toLowerCase()	Return the string in lowercase
4	String concat(String str)	Concatenate two strings
5	String toUpperCase()	Return the string in uppercase
6	String replace(char old, char new)	Replace all old characters with a new character
7	int indexOf(int ch)	Return index of specified character
8	String trim()	Remove starting and ending spaces of this string
9	int length()	Return the length of the string
10	boolean equalsIgnoreCase(String anotherString)	It compare two strings, ignoring their case considerations

StringBuffer

It is the same as the String class but is used to create mutable objects.
All methods are synchronized.
Multiple threads can use it.
It is initialized using the ‘new’ keyword.

Syntax:

StringBuffer sb = new StringBuffer("string");

Example:

package quipohouse;
class String_Buffer
{
    public static void main(String args[])
    {
        StringBuffer sb = new StringBuffer("Quipo");
        sb.append("House");
        System.out.println(sb);
    }
}

Output:

QuipoHouse

StringBuilder

It is also used to create mutable objects.
It is the same as the StringBuffer class but it is non-synchronized.
It is not safe to use in multiple threads.
It is initialized using the ‘new’ keyword.

Syntax:

StringBuilder sbr = new StringBuilder("string");

Example:

package quipohouse;
class String_Buffer
{
    public static void main(String args[])
    {
        StringBuilder sbr = new StringBuilder("Quipo");
        sbr.append("House");
        System.out.println(sbr);
    }
}

Output:

QuipoHouse

String vs StringBuffer vs StringBuilder

Topic	String	StringBuffer	StringBuilder
Storage	It uses Heap Memory and String Constant Pool	It uses Heap Memory	It uses Heap Memory
Object	It creates an immutable object	It creates a mutable object	It creates a mutable object
Memory	It occupies a large amount of memory	It occupies less amount memory	It occupies less amount memory
Thread safety	It is not thread-safe	Methods are synchronized so it is thread-safe	Methods are not synchronized so it is not thread-safe
Performance	Its performance is slow	Its performance is fast as compared to String	Its performance is fast as compared to StringBuffer
Use	If data does not change	If data changes frequently	If data changes frequently