Computer Applications

Differentiate between equals() and ==

Java String Handling

ICSE 2008

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Answer

equals()	==
It is a method	It is a relational operator
It is used to check if the contents of two strings are same or not	It is used to check if two variables refer to the same object in memory
Example: String s1 = new String("hello"); String s2 = new String("hello"); boolean res = s1.equals(s2); System.out.println(res); The output of this code snippet is true as contents of s1 and s2 are the same.	Example: String s1 = new String("hello"); String s2 = new String("hello"); boolean res = s1 == s2; System.out.println(res); The output of this code snippet is false as s1 and s2 point to different String objects.

Answered By

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Consider the following String array and give the output


String arr[]= {"DELHI", "CHENNAI", "MUMBAI", "LUCKNOW", "JAIPUR"}; 
System.out.println(arr[0].length() > arr[3].length()); 
System.out.print(arr[4].substring(0,3));

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Your friend is trying to write a program to find and display the frequency of vowels in a string. Due to confusion in the syntax of some of the statements, he could not complete the program and has left some places blank marked with ?1?, ?2?, ?3? and ?4? to be filled with expression/function. The incomplete program is shown below:

import java.util.*; 
class Vowels
{
  public static void main(String args[])
  {
    Scanner ...?1?... = new Scanner(System.in);
    String st;
    int i, b, v = 0;
    char chr;
    System.out.println("Enter a string");
    st = ............?2?............; // to input a string
    st = ............?3?...........; // to convert the string into uppercase
    b = st.length();
    for( i = 0 ; i < b ; i++)
    {
      chr = ............?4?............; // to extract a character
      if(chr == 'A' || chr == 'E' || chr == 'I' || chr == 'O' || chr == 'U')
        v = v + 1;
    }
    System.out.println("No. of Vowels = " + v);
  }
}

Based on the above discussion, answer the following questions:

(a) What expression/function will be filled in place of ?1?

(b) What expression/function will be filled in place of ?2?

(d) What expression/function will be filled in place of ?4?