ByteBuffer allocate() method in Java with Examples

The allocate() method of java.nio.ByteBuffer class is used to allocate a new byte buffer.

The new buffer’s position will be zero, its limit will be its capacity, its mark will be undefined, and each of its elements will be initialized to zero. It will have a backing array, and its array offset will be zero.

Syntax :

public static ByteBuffer allocate(int capacity)

Parameters: This method takes capacity, in bytes as parameter.

Return Value: This method returns the new byte buffer .

Throws: This method throws IllegalArgumentException, If the capacity is a negative integer

Below are the examples to illustrate the allocate() method:

Examples 1:

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

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

public class GFG {

    public static void main(String[] args)
    {

        // Declaring the capacity of the ByteBuffer
        int capacity = 4;

        // Creating the ByteBuffer
        try {

            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.allocate(capacity);

            // putting the int to byte typecast value
            // in ByteBuffer using putInt() method
            bb.put((byte)20);
            bb.put((byte)30);
            bb.put((byte)40);
            bb.put((byte)50);
            bb.rewind();

            // print the ByteBuffer
            System.out.println("Original ByteBuffer:  "
                               + Arrays.toString(bb.array()));
        }

        catch (IllegalArgumentException e) {

            System.out.println("IllegalArgumentException catched");
        }

        catch (ReadOnlyBufferException e) {

            System.out.println("ReadOnlyBufferException catched");
        }
    }
}

Output:

Original ByteBuffer:  [20, 30, 40, 50]

Examples 2:

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

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

public class GFG {

    public static void main(String[] args)
    {

        // Declaring the capacity with negative
        // value of the ByteBuffer
        int capacity = -4;

        // Creating the ByteBuffer
        try {

            // creating object of ByteBuffer
            // and allocating size capacity
            System.out.println("Trying to allocate negative"+
                                         " value in ByteBuffer");
            ByteBuffer bb = ByteBuffer.allocate(capacity);

            // putting int to byte typecast value
            // in ByteBuffer using putInt() method
            bb.put((byte)20);
            bb.put((byte)30);
            bb.put((byte)40);
            bb.put((byte)50);
            bb.rewind();

            // print the ByteBuffer
            System.out.println("Original ByteBuffer:  "
                               + Arrays.toString(bb.array()));
        }

        catch (IllegalArgumentException e) {

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

        catch (ReadOnlyBufferException e) {

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

Output:

Trying to allocate negative value in ByteBuffer
Exception thrown : java.lang.IllegalArgumentException