String in Java
Unlike many other languages that implement strings as character arrays, Java implements strings as an object of class java.lang.String.
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String are immutable objects in java.
Meaning of Immutability :-
We can’t change the sequence of Characters encapsulated in a String Object.
Each operation on that object will produce a new String object.
Creating String Objects :
Using new Keyword :
String str = new String( );
String str = new String( "india" );
Using String Literal :
String str = "bharat";
Construct String object from char array:
char [ ] ar = {'h', 'e', 'l', 'l', 'o'};
String str = new String( ar );When we create an object of String class using new operator, it creates String object in Heap memory area.
When we create an object of String class using String Literal, it creates String object in String Constant Pool area.
In Heap, we can create two or more objects of String class having identical character sequences.
In String Constant Pool, duplicate string objects are not allowed.
Example :
public class StringDemo { public static void main(String []ar) { //creating by string literal String s1="Java"; char ch[]={'P','r','o','w','e','s','s'}; //converting char array to string String s2=new String(ch); //creating by new keyword String s3=new String("App"); System.out.println(s1); System.out.println(s2); System.out.println(s3); } }OUTPUT :
Java Prowess App
Java String class methods :
The java.lang.String class provides so many methods to perform operations on String object.
You can check the list of all methods by typing the command on terminal (command prompt )
javap java.lang.String
SOME USEFUL METHODS ARE :
1. concat() - concatenates two String objects
String s1 = "Java"; String s2 = " Prowess"; String s3 = s1.concat(s2); System.out.print(s3); [OUTPUT :] Java Prowess
2. length() - returns the characters count available in string.
String s1 = "Indian"; int x = s1.length( ); System.out.print(x); [OUTPUT :] 6
3. toUpperCase, toLowerCase - changes the case from lower to upper and vice-versa.
String s1 = "hello"; String s2 = s1.toUpperCase( ); System.out.print(s2); [OUTPUT :] HELLO
4. indexOf() - returns the index of character in String if available , return -1 otherwise.
String s1 = "Java Prowess"; int y = s1.indexOf('P'); System.out.print(y); [OUTPUT :] 5
5. charAt() - returns character at specified index.
String s1 = "Java Prowess"; char ch = s1.charAt(5); System.out.print(ch); [OUTPUT :] P
6. equals() - compare two string and returns boolean
String s1 = "J2EE"; String s2 = "JEE"; boolean b = s1.equals(s2); System.out.printl(b); [OUTPUT :] false
7. equalsIgnoreCase() - compare two string ignore the case and returns boolean
String s1 = "J2EE"; String s2 = "J2Ee"; boolean b = s1.equalsIgnoreCase(s2); System.out.print(b); [OUTPUT :] true
8. subString() - return substring from the given index
String s1 = "Java Prowess"; //from given index to last index String s2 = s1.subString(5); OR //from given index to secondIndex-1 String s3 = s1.subString(5,7); System.out.println(s2); System.out.print(s3); [OUTPUT :] Prowess Pr
StringBuffer Class :
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java.lang.StringBuffer : StringBuffer is a peer class of String, that represents mutable type String objects on Heap memory area
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StringBuffer defines these three constructors:
StringBuffer( ) – Default Constructor
StringBuffer(int size) - int Defines size of String Object
StringBuffer(String str) – to get StringBuffer object from String object
Example :
StringBuffer sb1 = new StringBuffer( );
StringBuffer sb = new StringBuffer("abcd");
Next topic is exception-handling
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