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💡String:–

Generally string is a sequence of characters, but in java, strings are immutable objects. Immutable simply means  unmodifiable/unchangeable.

💡Creation of String object:-

1:- By string literal
2:- By new keyword

Feature	String Literal	String Class’s Constructor
Stored in string pool	Yes	No
Created at compile time	Yes	No
Can be modified	No	Yes
Can represent a string not known at compile time	No	Yes
Memory usage	Low	High
Access speed	Fast	Slow

💡1:- String literal:-

String s1=”Welcome”; //1 object createdString s2=”Welcome”; //no object will be created

Description:- When a String is created, JVM checks it in string constant pool if it exists it returns reference else string object is submitted to pool.

💡2:- By new keyword:-

String s=new String(“Welcome”);     //Creates 2 objectsString s1=new String(“Welcome”);   //1 object

Description:- new String object is created in nonpool(heap memory) and literal “Welcome” is created in string constant pool. The variable s is reference variable for object created in nonpool.

Methods of String class– There are many functions which can be performed on string such as concatenation, trim, split, substring etc.

💡String Buffer & String Builder –

Quick comparison of String, StringBuilder, and StringBuffer in Java:

Property	String	StringBuilder	StringBuffer
Class	String	StringBuilder	StringBuffer
Mutability	Immutable	Mutable	Mutable
Thread Safety	Thread-safe	Not thread-safe	Thread-safe
Performance	Slower	Faster	Slower
Methods	Fewer	More	Fewer
Use Cases	When the value of the string is not going to change	When the value of the string will be modified multiple times and thread-safety is not a concern	When the value of the string will be modified multiple times and thread-safety is a concern

Both classes are used to create mutable strings.

Unlike Strings these are stored in heap memory.

Both classes have same methods, but each method in StringBuffer is synchronized so StringBuffer is thread safe.

StringBuilder is fast in performance.

code samples are here
1-Mostly Used String methods-

package strn;
public class ExStrings {
public static void main(String[] args) {
String nameLiteral = "kuldeep"; // 1 object creation
String nameobject = new String("kaushik"); // 2 object creation
System.out.println(nameLiteral.charAt(4));
System.out.println(nameLiteral.concat(nameobject));
String[] arr1 = nameLiteral.split("d");
System.out.println(arr1[0] + " and " + arr1[1]);
System.out.println(nameLiteral.length());
String fortrim = " deep ";
System.out.println(fortrim);
System.out.println(fortrim.trim());
System.out.println(nameLiteral.equals(nameobject)); System.out.println(nameLiteral.indexOf("e"));
System.out.println(nameLiteral.isEmpty());
System.out.println(nameLiteral.length());
System.out.println(nameLiteral.substring(4));
System.out.println(nameLiteral.substring(2, 5));
System.out.println(nameLiteral.compareTo(nameobject));
System.out.println(nameLiteral.contains("ul"));
System.out.println(nameLiteral.replace("ul", "lu"));
}
}

Run this Program 

2-Mostly Used StringBuilder/StringBuffer methods-(both classes have same methods)

package strn;
public class ExStringB {
public static void main(String[] args) {
StringBuilder sb1=new StringBuilder("java");
System.out.println(sb1.reverse());
StringBuffer sb2=new StringBuffer("core");
System.out.println(sb2.reverse());
}
}

Run this Program 

Interview Questions —

• What is String in java?
• What is difference between String and String builder/buffer?