CharBuffer compact() method in Java

The compact() method of java.nio.CharBuffer Class is used to compact the given buffer.

The values between the buffer’s current position and its limit are copied to the beginning of the buffer. The buffer’s position is then set to n+1 and its limit is set to its capacity. The buffer’s position is set to the number of floats copied.

Syntax:

public abstract CharBuffer compact()

Return Value: This method returns the new CharBuffer with the same content as that of this buffer.

Exception: This method throws the ReadOnlyBufferException, If this buffer is read-only.

Below program illustrates the compact() method:

Example 1:

// Java program to demonstrate
// compact() method
import java.nio.*;
import java.util.*;

public class GFG {
    public static void main(String[] args)
    {

        // Declaring the capacity of the CharBuffer
        int capacity = 10;

        // Creating the CharBuffer

        // creating object of Intbuffer
        // and allocating size capacity
        CharBuffer ic = CharBuffer.allocate(capacity);

        // putting the value in Intbuffer
        ic.put('a');
        ic.put('b');
        ic.put('c');

        // print the CharBuffer
        System.out.println("Original CharBuffer: "
                           + Arrays.toString(ic.array()));

        System.out.println("Position: " + ic.position());

        System.out.println("limit: " + ic.limit());

        // Creating a compacted CharBuffer of same CharBuffer
        // using compact() method
        CharBuffer CharBuffer = ic.compact();

        // print the CharBuffer
        System.out.println("\nCompacted CharBuffer: "
                           + Arrays.toString(CharBuffer.array()));

        System.out.println("Position: " + CharBuffer.position());

        System.out.println("limit: " + CharBuffer.limit());

        // putting the value in compacted Intbuffer
        CharBuffer.put('g');

        // print the CharBuffer
        System.out.println("\nUpdated Compacted CharBuffer: "
                           + Arrays.toString(CharBuffer.array()));
        System.out.println("Position: " + CharBuffer.position());
        System.out.println("limit: " + CharBuffer.limit());
    }
}

Output:

Original CharBuffer: [a, b, c, , , , , , , ]
Position: 3
limit: 10

Compacted CharBuffer: [, , , , , , , , , ]
Position: 7
limit: 10

Updated Compacted CharBuffer: [, , , , , , , g, , ]
Position: 8
limit: 10

Example 2:

// Java program to demonstrate
// compact() method

import java.nio.*;
import java.util.*;

public class GFG {
    public static void main(String[] args)
    {

        // Declaring the capacity of the CharBuffer
        int capacity = 10;

        // Creating the CharBuffer
        try {

            // creating object of CharBuffer
            // and allocating size capacity
            CharBuffer cb = CharBuffer.allocate(capacity);

            // putting the value in CharBuffer
            cb.put('a');
            cb.put('b');
            cb.put('b');
            cb.rewind();

            // Creating a read-only copy of CharBuffer
            // using asReadOnlyBuffer() method
            CharBuffer cb1 = cb.asReadOnlyBuffer();

            // print the ReadOnlyBuffer
            System.out.print("ReadOnlyBuffer CharBuffer: ");
            while (cb1.hasRemaining())
                System.out.print(cb1.get() + ", ");
            System.out.println("");

            // print the Position of CharBuffer cb
            System.out.println("\nPosition: " + cb.position());

            // print the Limit of CharBuffer cb
            System.out.println("\nlimit: " + cb.limit());

            // Creating a compacted CharBuffer of same ReadOnlyBuffer
            // using compact() method
            System.out.println("\nTrying to compact the ReadOnlyBuffer cb1");
            CharBuffer CharBuffer = cb1.compact();
        }

        catch (IllegalArgumentException e) {

            System.out.println("Exception throws " + e);
        }

        catch (ReadOnlyBufferException e) {

            System.out.println("Exception throws " + e);
        }
    }
}

Output:

ReadOnlyBuffer CharBuffer: a, b, b, , , , , , , , 

Position: 0

limit: 10

Trying to compact the ReadOnlyBuffer cb1
Exception throws java.nio.ReadOnlyBufferException