public static CharBuffer allocate(int capacity)

// 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 CharBuffer
        char capacity = 10;
  
        // Creating the CharBuffer
  
        // creating object of Charbuffer
        // and allocating size capacity
        CharBuffer fb = CharBuffer.allocate(capacity);
  
        // putting the value in charbuffer
        fb.put('a');
        fb.put(3, 'b');
  
        // Printing the CharBuffer
        System.out.println("ChartBuffer: "
                           + Arrays.toString(fb.array()));
    }
}

ChartBuffer: [a, , , b, , , , , , ]

// 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 CharBuffer
        // by negative integer
        int capacity = -10;
  
        // Creating the CharBuffer
        try {
  
            // creating object of CharBuffer
            // and allocating size with negative integer
            System.out.println("Trying to allocate a negative integer");
  
            CharBuffer fb = CharBuffer.allocate(capacity);
        }
        catch (IllegalArgumentException e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

Trying to allocate a negative integer
Exception thrown: java.lang.IllegalArgumentException