Study Anytime Any Where We Will Open The Knowledge For You Anish Sir 24x7 Learning solution It Is Time to join JOB
09 December 2019

Study Anytime Any Where

09 December 2019

We Will Open The Knowledge For You

09 December 2019

Anish Sir 24x7 Learning solution

09 December 2019

It Is Time to join JOB

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Anish Sir

Anish Sir

"I am delighted once again to pen the welcome note to the Tosh!Yas Technologies ."

 Call +91 74 88 34 7779  | Email : anishsingh@live.com

Website URL: http://toshiyas.in
Monday, 24 July 2017 04:29

How to create Immutable class?

There are many immutable classes like String, Boolean, Byte, Short, Integer, Long, Float, Double etc. In short, all the wrapper classes and String class is immutable. We can also create immutable class by creating final class that have final data members as the example given below:

Example to create Immutable class

In this example, we have created a final class named Employee. It have one final datamember, a parameterized constructor and getter method.
 
  1. public final class Employee{  
  2. final String pancardNumber;  
  3.   
  4. public Employee(String pancardNumber){  
  5. this.pancardNumber=pancardNumber;  
  6. }  
  7.   
  8. public String getPancardNumber(){  
  9. return pancardNumber;  
  10. }  
  11.   
  12. }  

The above class is immutable because:

  • The instance variable of the class is final i.e. we cannot change the value of it after creating an object.
  • The class is final so we cannot create the subclass.
  • There is no setter methods i.e. we have no option to change the value of the instance variable.
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Monday, 24 July 2017 04:27

Difference between StringBuffer and StringBuilder

There are many differences between StringBuffer and StringBuilder. A list of differences between StringBuffer and StringBuilder are given below:

No. StringBuffer StringBuilder
1) StringBuffer is synchronized i.e. thread safe. It means two threads can't call the methods of StringBuffer simultaneously. StringBuilder is non-synchronized i.e. not thread safe. It means two threads can call the methods of StringBuilder simultaneously.
2) StringBuffer is less efficient than StringBuilder. StringBuilder is more efficient than StringBuffer.

StringBuffer Example

 
  1. public class BufferTest{  
  2.     public static void main(String[] args){  
  3.         StringBuffer buffer=new StringBuffer("hello");  
  4.         buffer.append("java");  
  5.         System.out.println(buffer);  
  6.     }  
  7. }  
hellojava

StringBuilder Example

 
  1. public class BuilderTest{  
  2.     public static void main(String[] args){  
  3.         StringBuilder builder=new StringBuilder("hello");  
  4.         builder.append("java");  
  5.         System.out.println(builder);  
  6.     }  
  7. }  
hellojava

Performance Test of StringBuffer and StringBuilder

Let's see the code to check the performance of StringBuffer and StringBuilder classes.

 
  1. public class ConcatTest{  
  2.     public static void main(String[] args){  
  3.         long startTime = System.currentTimeMillis();  
  4.         StringBuffer sb = new StringBuffer("Java");  
  5.         for (int i=0; i<10000; i++){  
  6.             sb.append("Tpoint");  
  7.         }  
  8.         System.out.println("Time taken by StringBuffer: " + (System.currentTimeMillis() - startTime) + "ms");  
  9.         startTime = System.currentTimeMillis();  
  10.         StringBuilder sb2 = new StringBuilder("Java");  
  11.         for (int i=0; i<10000; i++){  
  12.             sb2.append("Tpoint");  
  13.         }  
  14.         System.out.println("Time taken by StringBuilder: " + (System.currentTimeMillis() - startTime) + "ms");  
  15.     }  
  16. }  
Time taken by StringBuffer: 16ms
Time taken by StringBuilder: 0ms
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Monday, 24 July 2017 04:25

Difference between String and StringBuffer

There are many differences between String and StringBuffer. A list of differences between String and StringBuffer are given below:

No. String StringBuffer
1) String class is immutable. StringBuffer class is mutable.
2) String is slow and consumes more memory when you concat too many strings because every time it creates new instance. StringBuffer is fast and consumes less memory when you cancat strings.
3) String class overrides the equals() method of Object class. So you can compare the contents of two strings by equals() method. StringBuffer class doesn't override the equals() method of Object class.

Performance Test of String and StringBuffer

 
  1. public class ConcatTest{  
  2.     public static String concatWithString()    {  
  3.         String t = "Java";  
  4.         for (int i=0; i<10000; i++){  
  5.             t = t + "Tpoint";  
  6.         }  
  7.         return t;  
  8.     }  
  9.     public static String concatWithStringBuffer(){  
  10.         StringBuffer sb = new StringBuffer("Java");  
  11.         for (int i=0; i<10000; i++){  
  12.             sb.append("Tpoint");  
  13.         }  
  14.         return sb.toString();  
  15.     }  
  16.     public static void main(String[] args){  
  17.         long startTime = System.currentTimeMillis();  
  18.         concatWithString();  
  19.         System.out.println("Time taken by Concating with String: "+(System.currentTimeMillis()-startTime)+"ms");  
  20.         startTime = System.currentTimeMillis();  
  21.         concatWithStringBuffer();  
  22.         System.out.println("Time taken by Concating with  StringBuffer: "+(System.currentTimeMillis()-startTime)+"ms");  
  23.     }  
  24. }  
Time taken by Concating with String: 578ms
Time taken by Concating with  StringBuffer: 0ms

String and StringBuffer HashCode Test

As you can see in the program given below, String returns new hashcode value when you concat string but StringBuffer returns same.

 
  1. public class InstanceTest{  
  2.     public static void main(String args[]){  
  3.         System.out.println("Hashcode test of String:");  
  4.         String str="java";  
  5.         System.out.println(str.hashCode());  
  6.         str=str+"tpoint";  
  7.         System.out.println(str.hashCode());  
  8.    
  9.         System.out.println("Hashcode test of StringBuffer:");  
  10.         StringBuffer sb=new StringBuffer("java");  
  11.         System.out.println(sb.hashCode());  
  12.         sb.append("tpoint");  
  13.         System.out.println(sb.hashCode());  
  14.     }  
  15. }  
Hashcode test of String:
3254818
229541438
Hashcode test of StringBuffer:
118352462
118352462
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Monday, 24 July 2017 04:23

Java StringBuilder class

Java StringBuilder class is used to create mutable (modifiable) string. The Java StringBuilder class is same as StringBuffer class except that it is non-synchronized. It is available since JDK 1.5.

Important Constructors of StringBuilder class

Constructor Description
StringBuilder() creates an empty string Builder with the initial capacity of 16.
StringBuilder(String str) creates a string Builder with the specified string.
StringBuilder(int length) creates an empty string Builder with the specified capacity as length.

Important methods of StringBuilder class

Method Description
public StringBuilder append(String s) is used to append the specified string with this string. The append() method is overloaded like append(char), append(boolean), append(int), append(float), append(double) etc.
public StringBuilder insert(int offset, String s) is used to insert the specified string with this string at the specified position. The insert() method is overloaded like insert(int, char), insert(int, boolean), insert(int, int), insert(int, float), insert(int, double) etc.
public StringBuilder replace(int startIndex, int endIndex, String str) is used to replace the string from specified startIndex and endIndex.
public StringBuilder delete(int startIndex, int endIndex) is used to delete the string from specified startIndex and endIndex.
public StringBuilder reverse() is used to reverse the string.
public int capacity() is used to return the current capacity.
public void ensureCapacity(int minimumCapacity) is used to ensure the capacity at least equal to the given minimum.
public char charAt(int index) is used to return the character at the specified position.
public int length() is used to return the length of the string i.e. total number of characters.
public String substring(int beginIndex) is used to return the substring from the specified beginIndex.
public String substring(int beginIndex, int endIndex) is used to return the substring from the specified beginIndex and endIndex.

Java StringBuilder Examples

Let's see the examples of different methods of StringBuilder class.

1) StringBuilder append() method

The StringBuilder append() method concatenates the given argument with this string.

 
  1. class StringBuilderExample{  
  2. public static void main(String args[]){  
  3. StringBuilder sb=new StringBuilder("Hello ");  
  4. sb.append("Java");//now original string is changed  
  5. System.out.println(sb);//prints Hello Java  
  6. }  
  7. }  

2) StringBuilder insert() method

The StringBuilder insert() method inserts the given string with this string at the given position.

 
  1. class StringBuilderExample2{  
  2. public static void main(String args[]){  
  3. StringBuilder sb=new StringBuilder("Hello ");  
  4. sb.insert(1,"Java");//now original string is changed  
  5. System.out.println(sb);//prints HJavaello  
  6. }  
  7. }  

3) StringBuilder replace() method

The StringBuilder replace() method replaces the given string from the specified beginIndex and endIndex.

 
  1. class StringBuilderExample3{  
  2. public static void main(String args[]){  
  3. StringBuilder sb=new StringBuilder("Hello");  
  4. sb.replace(1,3,"Java");  
  5. System.out.println(sb);//prints HJavalo  
  6. }  
  7. }  

4) StringBuilder delete() method

The delete() method of StringBuilder class deletes the string from the specified beginIndex to endIndex.

 
  1. class StringBuilderExample4{  
  2. public static void main(String args[]){  
  3. StringBuilder sb=new StringBuilder("Hello");  
  4. sb.delete(1,3);  
  5. System.out.println(sb);//prints Hlo  
  6. }  
  7. }  

5) StringBuilder reverse() method

The reverse() method of StringBuilder class reverses the current string.

 
  1. class StringBuilderExample5{  
  2. public static void main(String args[]){  
  3. StringBuilder sb=new StringBuilder("Hello");  
  4. sb.reverse();  
  5. System.out.println(sb);//prints olleH  
  6. }  
  7. }  

6) StringBuilder capacity() method

The capacity() method of StringBuilder class returns the current capacity of the Builder. The default capacity of the Builder is 16. If the number of character increases from its current capacity, it increases the capacity by (oldcapacity*2)+2. For example if your current capacity is 16, it will be (16*2)+2=34.

 
  1. class StringBuilderExample6{  
  2. public static void main(String args[]){  
  3. StringBuilder sb=new StringBuilder();  
  4. System.out.println(sb.capacity());//default 16  
  5. sb.append("Hello");  
  6. System.out.println(sb.capacity());//now 16  
  7. sb.append("java is my favourite language");  
  8. System.out.println(sb.capacity());//now (16*2)+2=34 i.e (oldcapacity*2)+2  
  9. }  
  10. }  

7) StringBuilder ensureCapacity() method

The ensureCapacity() method of StringBuilder class ensures that the given capacity is the minimum to the current capacity. If it is greater than the current capacity, it increases the capacity by (oldcapacity*2)+2. For example if your current capacity is 16, it will be (16*2)+2=34.

 
  1. class StringBuilderExample7{  
  2. public static void main(String args[]){  
  3. StringBuilder sb=new StringBuilder();  
  4. System.out.println(sb.capacity());//default 16  
  5. sb.append("Hello");  
  6. System.out.println(sb.capacity());//now 16  
  7. sb.append("java is my favourite language");  
  8. System.out.println(sb.capacity());//now (16*2)+2=34 i.e (oldcapacity*2)+2  
  9. sb.ensureCapacity(10);//now no change  
  10. System.out.println(sb.capacity());//now 34  
  11. sb.ensureCapacity(50);//now (34*2)+2  
  12. System.out.println(sb.capacity());//now 70  
  13. }  
  14. }  

 

 

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Monday, 24 July 2017 04:20

Java StringBuffer class

Java StringBuffer class is used to create mutable (modifiable) string. The StringBuffer class in java is same as String class except it is mutable i.e. it can be changed.

Note: Java StringBuffer class is thread-safe i.e. multiple threads cannot access it simultaneously. So it is safe and will result in an order.

Important Constructors of StringBuffer class

Constructor Description
StringBuffer() creates an empty string buffer with the initial capacity of 16.
StringBuffer(String str) creates a string buffer with the specified string.
StringBuffer(int capacity) creates an empty string buffer with the specified capacity as length.

Important methods of StringBuffer class

Modifier and Type Method Description
public synchronized StringBuffer append(String s) is used to append the specified string with this string. The append() method is overloaded like append(char), append(boolean), append(int), append(float), append(double) etc.
public synchronized StringBuffer insert(int offset, String s) is used to insert the specified string with this string at the specified position. The insert() method is overloaded like insert(int, char), insert(int, boolean), insert(int, int), insert(int, float), insert(int, double) etc.
public synchronized StringBuffer replace(int startIndex, int endIndex, String str) is used to replace the string from specified startIndex and endIndex.
public synchronized StringBuffer delete(int startIndex, int endIndex) is used to delete the string from specified startIndex and endIndex.
public synchronized StringBuffer reverse() is used to reverse the string.
public int capacity() is used to return the current capacity.
public void ensureCapacity(int minimumCapacity) is used to ensure the capacity at least equal to the given minimum.
public char charAt(int index) is used to return the character at the specified position.
public int length() is used to return the length of the string i.e. total number of characters.
public String substring(int beginIndex) is used to return the substring from the specified beginIndex.
public String substring(int beginIndex, int endIndex) is used to return the substring from the specified beginIndex and endIndex.

What is mutable string

A string that can be modified or changed is known as mutable string. StringBuffer and StringBuilder classes are used for creating mutable string.

1) StringBuffer append() method

The append() method concatenates the given argument with this string.

 
  1. class StringBufferExample{  
  2. public static void main(String args[]){  
  3. StringBuffer sb=new StringBuffer("Hello ");  
  4. sb.append("Java");//now original string is changed  
  5. System.out.println(sb);//prints Hello Java  
  6. }  
  7. }  

2) StringBuffer insert() method

The insert() method inserts the given string with this string at the given position.

 
  1. class StringBufferExample2{  
  2. public static void main(String args[]){  
  3. StringBuffer sb=new StringBuffer("Hello ");  
  4. sb.insert(1,"Java");//now original string is changed  
  5. System.out.println(sb);//prints HJavaello  
  6. }  
  7. }  

3) StringBuffer replace() method

The replace() method replaces the given string from the specified beginIndex and endIndex.

 
  1. class StringBufferExample3{  
  2. public static void main(String args[]){  
  3. StringBuffer sb=new StringBuffer("Hello");  
  4. sb.replace(1,3,"Java");  
  5. System.out.println(sb);//prints HJavalo  
  6. }  
  7. }  

4) StringBuffer delete() method

The delete() method of StringBuffer class deletes the string from the specified beginIndex to endIndex.

 
  1. class StringBufferExample4{  
  2. public static void main(String args[]){  
  3. StringBuffer sb=new StringBuffer("Hello");  
  4. sb.delete(1,3);  
  5. System.out.println(sb);//prints Hlo  
  6. }  
  7. }  

5) StringBuffer reverse() method

The reverse() method of StringBuilder class reverses the current string.

 
  1. class StringBufferExample5{  
  2. public static void main(String args[]){  
  3. StringBuffer sb=new StringBuffer("Hello");  
  4. sb.reverse();  
  5. System.out.println(sb);//prints olleH  
  6. }  
  7. }  

6) StringBuffer capacity() method

The capacity() method of StringBuffer class returns the current capacity of the buffer. The default capacity of the buffer is 16. If the number of character increases from its current capacity, it increases the capacity by (oldcapacity*2)+2. For example if your current capacity is 16, it will be (16*2)+2=34.

 
  1. class StringBufferExample6{  
  2. public static void main(String args[]){  
  3. StringBuffer sb=new StringBuffer();  
  4. System.out.println(sb.capacity());//default 16  
  5. sb.append("Hello");  
  6. System.out.println(sb.capacity());//now 16  
  7. sb.append("java is my favourite language");  
  8. System.out.println(sb.capacity());//now (16*2)+2=34 i.e (oldcapacity*2)+2  
  9. }  
  10. }  

7) StringBuffer ensureCapacity() method

The ensureCapacity() method of StringBuffer class ensures that the given capacity is the minimum to the current capacity. If it is greater than the current capacity, it increases the capacity by (oldcapacity*2)+2. For example if your current capacity is 16, it will be (16*2)+2=34.

 
  1. class StringBufferExample7{  
  2. public static void main(String args[]){  
  3. StringBuffer sb=new StringBuffer();  
  4. System.out.println(sb.capacity());//default 16  
  5. sb.append("Hello");  
  6. System.out.println(sb.capacity());//now 16  
  7. sb.append("java is my favourite language");  
  8. System.out.println(sb.capacity());//now (16*2)+2=34 i.e (oldcapacity*2)+2  
  9. sb.ensureCapacity(10);//now no change  
  10. System.out.println(sb.capacity());//now 34  
  11. sb.ensureCapacity(50);//now (34*2)+2  
  12. System.out.println(sb.capacity());//now 70  
  13. }  
  14. }  

 

 

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Monday, 24 July 2017 04:17

Java String class methods

The java.lang.String class provides a lot of methods to work on string. By the help of these methods, we can perform operations on string such as trimming, concatenating, converting, comparing, replacing strings etc.

Java String is a powerful concept because everything is treated as a string if you submit any form in window based, web based or mobile application.

Let's see the important methods of String class.

Java String toUpperCase() and toLowerCase() method

The java string toUpperCase() method converts this string into uppercase letter and string toLowerCase() method into lowercase letter.

 
  1. String s="Sachin";  
  2. System.out.println(s.toUpperCase());//SACHIN  
  3. System.out.println(s.toLowerCase());//sachin  
  4. System.out.println(s);//Sachin(no change in original)  
SACHIN
sachin
Sachin

Java String trim() method

The string trim() method eliminates white spaces before and after string.

 
  1. String s="  Sachin  ";  
  2. System.out.println(s);//  Sachin    
  3. System.out.println(s.trim());//Sachin  
  Sachin  
Sachin

Java String startsWith() and endsWith() method

 
  1. String s="Sachin";  
  2.  System.out.println(s.startsWith("Sa"));//true  
  3.  System.out.println(s.endsWith("n"));//true  
true
true

Java String charAt() method

The string charAt() method returns a character at specified index.

 
  1. String s="Sachin";  
  2. System.out.println(s.charAt(0));//S  
  3. System.out.println(s.charAt(3));//h  
S
h

Java String length() method

The string length() method returns length of the string.

 
  1. String s="Sachin";  
  2. System.out.println(s.length());//6  
6

Java String intern() method

A pool of strings, initially empty, is maintained privately by the class String.

When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the equals(Object) method, then the string from the pool is returned. Otherwise, this String object is added to the pool and a reference to this String object is returned.

 
  1. String s=new String("Sachin");  
  2. String s2=s.intern();  
  3. System.out.println(s2);//Sachin  
Sachin

Java String valueOf() method

The string valueOf() method coverts given type such as int, long, float, double, boolean, char and char array into string.

 
  1. int a=10;  
  2. String s=String.valueOf(a);  
  3. System.out.println(s+10);  

Output:

1010

Java String replace() method

The string replace() method replaces all occurrence of first sequence of character with second sequence of character.

 
  1. String s1="Java is a programming language. Java is a platform. Java is an Island.";    
  2. String replaceString=s1.replace("Java","Kava");//replaces all occurrences of "Java" to "Kava"    
  3. System.out.println(replaceString);    

Output:

Kava is a programming language. Kava is a platform. Kava is an Island.

 

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Monday, 24 July 2017 04:11

Substring in Java

A part of string is called substring. In other words, substring is a subset of another string. In case of substring startIndex is inclusive and endIndex is exclusive.

Note: Index starts from 0.

You can get substring from the given string object by one of the two methods:

  1. public String substring(int startIndex): This method returns new String object containing the substring of the given string from specified startIndex (inclusive).
  2. public String substring(int startIndex, int endIndex): This method returns new String object containing the substring of the given string from specified startIndex to endIndex.

In case of string:

  • startIndex: inclusive
  • endIndex: exclusive

Let's understand the startIndex and endIndex by the code given below.

 
  1. String s="hello";  
  2. System.out.println(s.substring(0,2));//he  

In the above substring, 0 points to h but 2 points to e (because end index is exclusive).

Example of java substring

 
  1. public class TestSubstring{  
  2.  public static void main(String args[]){  
  3.    String s="SachinTendulkar";  
  4.    System.out.println(s.substring(6));//Tendulkar  
  5.    System.out.println(s.substring(0,6));//Sachin  
  6.  }  
  7. }  
Tendulkar
Sachin
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Monday, 24 July 2017 04:09

String Concatenation in Java

In java, string concatenation forms a new string that is the combination of multiple strings. There are two ways to concat string in java:

  1. By + (string concatenation) operator
  2. By concat() method

1) String Concatenation by + (string concatenation) operator

Java string concatenation operator (+) is used to add strings. For Example:

 
  1. class TestStringConcatenation1{  
  2.  public static void main(String args[]){  
  3.    String s="Sachin"+" Tendulkar";  
  4.    System.out.println(s);//Sachin Tendulkar  
  5.  }  
  6. }  
Output:Sachin Tendulkar

The Java compiler transforms above code to this:

 
  1. String s=(new StringBuilder()).append("Sachin").append(" Tendulkar).toString();  

In java, String concatenation is implemented through the StringBuilder (or StringBuffer) class and its append method. String concatenation operator produces a new string by appending the second operand onto the end of the first operand. The string concatenation operator can concat not only string but primitive values also. For Example:

 
  1. class TestStringConcatenation2{  
  2.  public static void main(String args[]){  
  3.    String s=50+30+"Sachin"+40+40;  
  4.    System.out.println(s);//80Sachin4040  
  5.  }  
  6. }  
80Sachin4040

Note: After a string literal, all the + will be treated as string concatenation operator.

2) String Concatenation by concat() method

The String concat() method concatenates the specified string to the end of current string. Syntax:

 
  1. public String concat(String another)  

Let's see the example of String concat() method.

 
  1. class TestStringConcatenation3{  
  2.  public static void main(String args[]){  
  3.    String s1="Sachin ";  
  4.    String s2="Tendulkar";  
  5.    String s3=s1.concat(s2);  
  6.    System.out.println(s3);//Sachin Tendulkar  
  7.   }  
  8. }  
Sachin Tendulkar
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Monday, 24 July 2017 04:06

Java String compare

We can compare string in java on the basis of content and reference.

It is used in authentication (by equals() method), sorting (by compareTo() method), reference matching (by == operator) etc.

There are three ways to compare string in java:

  1. By equals() method
  2. By = = operator
  3. By compareTo() method

1) String compare by equals() method

The String equals() method compares the original content of the string. It compares values of string for equality. String class provides two methods:

  • public boolean equals(Object another) compares this string to the specified object.
  • public boolean equalsIgnoreCase(String another) compares this String to another string, ignoring case.
 
  1. class Teststringcomparison1{  
  2.  public static void main(String args[]){  
  3.    String s1="Sachin";  
  4.    String s2="Sachin";  
  5.    String s3=new String("Sachin");  
  6.    String s4="Saurav";  
  7.    System.out.println(s1.equals(s2));//true  
  8.    System.out.println(s1.equals(s3));//true  
  9.    System.out.println(s1.equals(s4));//false  
  10.  }  
  11. }  
Output:true
       true
       false
 
  1. class Teststringcomparison2{  
  2.  public static void main(String args[]){  
  3.    String s1="Sachin";  
  4.    String s2="SACHIN";  
  5.   
  6.    System.out.println(s1.equals(s2));//false  
  7.    System.out.println(s1.equalsIgnoreCase(s3));//true  
  8.  }  
  9. }  
Output:false
       true
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Monday, 24 July 2017 04:04

Immutable String in Java

In java, string objects are immutable. Immutable simply means unmodifiable or unchangeable.

Once string object is created its data or state can't be changed but a new string object is created.

Let's try to understand the immutability concept by the example given below:

 
  1. class Testimmutablestring{  
  2.  public static void main(String args[]){  
  3.    String s="Sachin";  
  4.    s.concat(" Tendulkar");//concat() method appends the string at the end  
  5.    System.out.println(s);//will print Sachin because strings are immutable objects  
  6.  }  
  7. }  

Test it Now

Output:Sachin

Now it can be understood by the diagram given below. Here Sachin is not changed but a new object is created with sachintendulkar. That is why string is known as immutable.

Heap diagram

As you can see in the above figure that two objects are created but s reference variable still refers to "Sachin" not to "Sachin Tendulkar".

But if we explicitely assign it to the reference variable, it will refer to "Sachin Tendulkar" object.For example:

 
  1. class Testimmutablestring1{  
  2.  public static void main(String args[]){  
  3.    String s="Sachin";  
  4.    s=s.concat(" Tendulkar");  
  5.    System.out.println(s);  
  6.  }  
  7. }  

Test it Now

Output:Sachin Tendulkar

In such case, s points to the "Sachin Tendulkar". Please notice that still sachin object is not modified.

Why string objects are immutable in java?

Because java uses the concept of string literal.Suppose there are 5 reference variables,all referes to one object "sachin".If one reference variable changes the value of the object, it will be affected to all the reference variables. That is why string objects are immutable in java.
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