Strings in Java

Java Strings

A String variable contains a collection of characters surrounded by double quotes. Strings in Java are Objects that are backed internally by a char array.

Syntax for declaring a string<String_Type> <string_variable> = “<sequence_of_string>”;
ExampleString str = "RAKESH";

Memory allotment of String
Whenever a String Object is created, two objects will be created- one in the Heap Area and another in the String constant pool and the String object reference always points to heap area object.
The Java string constant pool is an area in heap memory where Java stores literal string values. The heap memory is a run time data area from which the memory for all java class instances and arrays is allocated.

1. Using string literal Example: String s = “java”;
A string written inside double quotes is called string literal. Whenever we create string literal the JVM checks string constant pool. If the string is already present in pool then its reference is fetched. If the string is not present in pool then a new string object is created in the pool.

2. Using new keyword Example: String s = new String(“java”);
When we create string using new keyword it goes to heap.

String Length

Using length method we can found length of a string.
Syntax:type var-name[]=new type[size];
Example1
String txt = "RK TUTORIALS"; System.out.println("The length of the txt string is: " + txt.length());Example2

Example2

import java.io.*;
import java.lang.*;
public class Mystring {
   public static void main(String[] args) {
    String s=new String("Rakesh Kumar");
     System.out.println("Length="+s.length());
  }
}

Output

Length=12

Some useful String Methods

The String class has a set of built-in methods that we can use on strings.

Method	Description	Return Type
charAt()	Returns the character at the specified index (position)	char
contains()	Checks whether a string contains a sequence of characters	boolean
contentEquals()	Checks whether a string contains the exact same sequence of characters of the specified CharSequence or StringBuffer	boolean
equals()	Compares two strings. Returns true if the strings are equal, and false if not	boolean
indexOf()	Returns the position of the first found occurrence of specified characters in a string	int
isEmpty()	Checks whether a string is empty or not	boolean
length()	Returns the length of a specified string	int
substring()	Extracts the characters from a string, beginning at a specified start position, and through the specified number of character	String
toLowerCase()	Converts a string to lower case letters	String
toString()	Returns the value of a String object	String
toUpperCase()	Converts a string to upper case letters	String
trim()	Removes whitespace from both ends of a string	String

Example-Find out total length with sapce, without space, number of vowels and consonants of given string.

import java.util.Scanner;
import java.lang.*;
class vowelcons
{
 public static void main(String[] argv)
 {
  Scanner obj=new Scanner(System.in);
  System.out.println("Enter any String");
  String str=obj.nextLine();
  int i,c=0,s=0,l,lw,con;
  l=str.length();
  for(i=0;i<l;i++)   {
   if(str.charAt(i)=='a'||str.charAt(i)=='e'||
str.charAt(i)=='i'||str.charAt(i)=='o'||
str.charAt(i)=='u')
   {
    c++;
    }
   else if(str.charAt(i)==' ')
   {
    s++;
   }
  }
  lw=l-s;
  con=lw-c;
  System.out.println("Total length with space="+l);
  System.out.println("Total length without space="+lw);
  System.out.println("No. of vowels="+c);
  System.out.println("No. of consonants="+con);
 }
}

Output

   Enter any string
   Rakesh Kumar
   Total length with space=12
   Total length without space=11
   No. of vowels=4
   No. of consonants7

Example-Enter message then print it in shortened from.

import java.util.Scanner;
import java.lang.Math;
class strsms{
  public static void main (String str[]){
  Scanner scan = new Scanner(System.in);
  System.out.println("Type the message to be shortened.");
  String message = scan.nextLine();
  int messageLength = message.length();
  int messageVowels = 0;
  String newMessage = "";
  int repeat = 0;
  int total = 0;
  if (messageLength < 10) {
   System.out.println("This doesn't need shortening!");
  } else {
  message = message.toLowerCase();
  newMessage = newMessage + message.charAt(0);
  for (int i = 1; i < messageLength; i++) {
   if (message.charAt(i)== 'a' ||
    message.charAt(i)== 'e' ||
   message.charAt(i)== 'i' ||
   message.charAt(i)== 'o' ||
   message.charAt(i)== 'u') {
     if (message.charAt(i-1) == ' '){
     newMessage = newMessage + message.charAt(i);
    }
    else {
      messageVowels++;
    }
    } else {
    if (message.charAt(i) != message.charAt(i-1)) {
    newMessage = newMessage + message.charAt(i);
  }
   else {
     repeat++;
    }
  }
}
total = repeat + messageVowels;
System.out.println("Shortened message: " + newMessage);
}
}
}