Implement a program to accomplish the following task using string / string Buffer class.

In this program, we will do the following:
  1. Accept a password from user.
  2. Check if password is correct then display "Good" Else display "Incorrect password"
  3. Append the password with the string "Welcome to java!!!"
  4. Display the password in reverse order.
  5. Replace the character '!' in password with "*" character.
We use String class and StringBuffer class to accomplish this task. The String class represents character strings. All string literals in Java programs, such as "abc", are implemented as instances of this class. Strings are immutable. Strings are constant; their values cannot be changed after they are created. For example:
String str = "abc";    // Creates a string literal
String str = new String("abc");

StringBuffer class is like a String, but can be modified. StringBuffer class is mutable. StringBuffer is fast and consumes less memory when you concat strings. For example,
// Constructs string buffer with no characters in it 
// and an initial capacity of 16 characters.
StringBuffer  s1 = new StringBuffer( );    

// Constructs a string buffer that contains the three characters.  
// The initial capacity of the string buffer is 16 plus 
// the length of the "abc" string in short it is 19. 
StringBuffer s2 = new StringBuffer("abc");

We have used the following methods of String class:
  • compareTo(String anotherString) : It compares two strings lexicographically.
  • replace(char oldChar, char newChar) : Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
We have used the following methods of StringBuffer class:
  • append(String str) : It appends the specified string to the character sequence.
  • reverse( ) : It causes the character sequence to be replaced by the reverse of the sequence.

import java.lang.*;

class StringActivity {
 public static void main(String args[]) throws IOException {
  BufferedReader br = new BufferedReader(new InputStreamReader(;
  String s1 = "admin!";
  String s2;
  System.out.println ("Enter Password");
  s2 = br.readLine();
  if(s1.compareTo(s2)==0) {
   System.out.println ("Good");
  else {
   System.out.println ("Password is incorrect");
  String s3 = "Welcome to Java!!!";
  StringBuffer sb = new StringBuffer(s1);
  System.out.println ("Appended Password = "+sb);
  StringBuffer s4 = new StringBuffer(s1);
  System.out.println ("String in Reverse Order = "+s4);
  System.out.println ("Replaced '!' with '*' = "+s1.replace('!','*')); 
C:\>java StringActivity
Enter Password
Appended Password = admin!Welcome to Java!!!
String in Reverse Order = !nimda
Replaced '!' with '*' = admin*

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