StringBuffer Class

StringBuffer Class

The StringBuffer is a class which is alternative to the String class. But StringBuffer class is more flexible to use than the String class. That means, using StringBuffer we can insert some components to the existing string or modify the existing string but in case of String class once the string is defined then it remains fixed. The StringBuffer and the StringBuilder are almost one and the same. The StringBuilder or StringBuffer have three constructors and 30 methods. Following are some simple methods used for StringBuffer –

Ex. 4.11.1: Write a Java Program illustrating the difference between the capacity and length function of StringBuffer.

Sol. :

Java Program [StringBuffDemo1.java]

public class StringBuffDemo1{

public static void main(String args[])

{

StringBuffer str=new StringBuffer("Java");

System.out.println("The String Buffer is "+str);

System.out.println("The length is "+str.length());

System.out.println("The capacity is"+ str.capacity());-

}

}

Output

F:\test>javac StringBuffDemo1.java

F:\test>java StringBuffDemo1

The String Buffer is Java

The length is 4

The capacity is 20

Program Explanation

Using the StringBuffer/StringBuilder class, we can create a buffer of characters. The length function returns the number of characters in the string and the capacity function returns the number of characters in the string +16 additional characters.

Ex. 4.11.2: Write a Java program, to convert the string 'Great' to a new string 'God'.

Sol. :

public class StringBuffDemo2{

public static void main(String args[])

{

StringBuffer str=new StringBuffer("Great");

System.out.println("The String is: "+str);

str.setCharAt(1,'o');'

str.setCharAt(2,'d');

str.setLength(3);

System.out.println("Now the String is: "+str);

}

}

Output

F:\test>javac StringBuffDemo2.java

F:\test>java StringBuffDemo2

The String is: Great

Now the String is: God

Program Explanation

In above program, we have to replace certain characters by new characters and the length of the string needs to be changed. For that purpose, there are two methods defined in StringBuffer and those are - setCharAt and setLength.

The setCharAt method, replaces the desired character by a new character.

setChar(1,'o');

Similarly, there is a setLength function which sets the length of the string. The string 'Great' has a length 5. To convert this string to a new string say 'God', the length is set to 3. The above given output simplifies the program.

Ex. 4.4.3 Write a simple Java program to append the string "God" by the string "is Great" and then append an exclamation mark to the complete string.

Sol.:

Java Program [StringBuffDemo3.java]

public class StringBuffDemo3{

public static void main(String args[])

{

StringBuffer str=new StringBuffer("God");

System.out.println("Initially the String is: "+str);

str.append(" is Great");

str.append("!");

System.out.println("Now the String is: "+str);

}

}

Output

F:\test>javac StringBuffDemo3.java

F:\test>java StringBuffDemo3

Initially the String is: God

Now the String is: God is Great!

Program Explanation

The append method is used to insert the string at the end of a given string. In case of String class the + operator is used to append the string to the existing string. Using append method we can append character string, numeric value or any object.

Ex. 4.11.4 Write a Java program to insert a string "FRIEND" in the given string "----in need is a in deed".

Sol.:

Java Program[StringBuffDemo4.java]

public class StringBuffDemo4{

public static void main(String args[])

{

StringBuffer str=new StringBuffer(" in need is a in deed");

StringBuffer new_str=new StringBuffer(" FRIEND");

System.out.println("Initially the String is: "+str);

str.insert(13,new_str);

str.insert(0,new_str);

System.out.println("Now the String is: "+str);

}

}

Output

F:\test>javac StringBuffDemo4.java

F:\test>java StringBuffDemo4

Initially the String is: in need is a in deed

Now the String is: FRIEND in need is a FRIEND in deed

F:\test>

Program Explanation

Using the insert method, the string or numeric value or any character can be inserted at the specified location in the given string. The program is self explanatory.

Ex. 4.11.5 Write a simple Java program to check the palindrome of the given string.

Sol. :

Java Program [StringBuffDemo5.java]

public class StringBuffDemo5{

public static void main(String args[])

{

String str1=new String("Java");

StringBuffer str2=new StringBuffer(str1);

str2.reverse();

System.out.println("Initially the String is: "+str1);

System.out.println("Reversed String is: "+str2);

if(str1.equals(str2.toString())) //checks if str1=str2

System.out.println("This string is palindrome");

else

System.out.println("This string is not palindrome");

}

}

Output

F:\test>javac StringBuffDemo5.java

F:\test>java StringBuffDemo5

Initially the String is: Java

Reversed String is: avaJ

This string is not palindrome

Ex. 4.11.6 : Write a simple Java program to change the string "impossible" to "possible".

Sol.:

Java Program [StringBuffDemo6.java]

public class StringBuffDemo6{

public static void main(String args[])

{

StringBuffer str1 = new StringBuffer("Impossible");

System.out.print("The word "+str1);

str1.delete(0,2);

System.out.println(" is changed to "+str1);

}

}

Output

F:\test>javac StringBuffDemo6.java

F:\test>java StringBuffDemo6

The String Impossible is changed to possible

Program Explanation

In above program, we have used the method delete for deleting the some characters. The first argument denotes the starting character and the second character denotes the ending character.