STRINGS

Before going into programs a small introduction on Strings

 

STRINGS:-

1.String is a class in Java

2.String means collection of characters

3.String is a sequence of characters enclosed in double Quotes.

4.Java Strings are sequence of Unicode characters

5.String class produces Immutable objects.

6.String class does not have a methods that let you change a characters in an existing String.

7.It is like number 5 , the String "HELLO" we cannot change it.

Sting Objects can be created in two ways

 

1. without using new operator

 

            String str1="javainchennai";

2. with using new operator

            String str2=new String("javainchennai");

The memory space is divided in to two parts

1.constant area

2.non-constant area       

If you create object without using new operator this will be saved in constant area

          (e.g)   String str1="javainchennai";

If you create object with using new operator this will be saved in non-constant area

          (e.g)  String str2=new String("javainchennai");

Here Constant area will not allow duplicates

 where as non-constant area will allow duplicates. 

Do Remember inside a String class the toString() method is  overided. Here if you try to print reference variable

                 String s1="javainchennai";

                 System.out.println(s1);

         The output is javainchennai   instead of String@ff2201(classname @ hexadecimal value)

equals() method also overrided to check 2 objects based on the value(content) it contains

Observe the program carefully and read the explanation:-

1.package com.vinodh;

2.public class StringTest {

3.    public static void main(String[] args) {

4.        String str1="javainchennai";

5.        String str2="javainchennai";

6.        String str3=new String("javainchennai");

7.        String str4=new String("javainchennai");

8.        System.out.println(str1==str2);

9.        System.out.println(str1==str3);

10.      System.out.println(str2==str3);

11.      System.out.println(str3==str4);

12.      System.out.println(str1.equals(str2));

13.      System.out.println(str1.equals(str3));

14.      System.out.println(str2.equals(str3));

15.      System.out.println(str3.equals(str4));

16.    }

17.   }

 

output:-

true

false

false

false

true

true

true

true

 

Explanation:-

 

If you say 5==5 is true, here two are primitive literals so == operator(checks content) prints true.

If you use == operator to compare two object references it will see whether both references are pointing to same object or different.

If both references are pointing to same object it(== operator) returns true otherwise false.

observe line4 and line5 ,here actually I created String object without using new operator so, str1 and str2 both references are pointing 

to same object (javainchennai). (constant area will not allow duplicates)

so, str1==str2 returns true.

observe line4 and line5 ,here actually I created String object by using new operator so, str3 and str4 both references are pointing to 

different objects (javainchennai).(non constant area allows duplicates).

So, str3==str4 returns false.

Observe the same effect with equals() method it returns true all time .(because it is overrided to compare based on content inside object)

 

PROGRAMS:-

1.public class StringTest {

2.    public static void main(String[] args) {

3.                            System.out.println(3+5);

4.                            System.out.println("3"+5);

5.                            System.out.println(3+"555");

6.                            System.out.println(3+2+5+"4444");

7.                            System.out.println("35"+111+"99");

8.                            System.out.println("42"+11+32+"77");

9.                            System.out.println("100"+"222");

   }

}

OUTPUT:-

8

35

3555

104444

3511199

42113277

100222

Explanation:-

In Java there is no operator overloading concept.

+ is the only one operator overloaded to add 2 integers as well as 2 strings

In the above example we added 2 primitives that is common ,

when we added String with any primitives only String object is produced.

observe the output of lines 6,7,8,9.