DoubleBuffer compact() method in Java With Examples

Last Updated : 04 Dec, 2018

The compact() method of java.nio.DoubleBuffer 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 DoubleBuffer compact()

Return Value: This method returns the new DoubleBuffer 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:

Examples 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 DoubleBuffer 
        int capacity = 10; 
  
        // Creating the DoubleBuffer 
  
        // creating object of Doublebuffer 
        // and allocating size capacity 
        DoubleBuffer db = DoubleBuffer.allocate(capacity); 
  
        // putting the value in Doublebuffer 
        db.put(8.56F); 
        db.put(9.61F); 
        db.put(9.61F); 
  
        // print the DoubleBuffer 
        System.out.println("Original DoubleBuffer: "
                           + Arrays.toString(db.array())); 
  
        System.out.println("Position: " + db.position()); 
  
        System.out.println("limit: " + db.limit()); 
  
        // Creating a compacted  DoubleBuffer of same DoubleBuffer 
        // using compact() method 
        DoubleBuffer DoubleBuffer = db.compact(); 
  
        // print the DoubleBuffer 
        System.out.println("\nCompacted DoubleBuffer: "
                           + Arrays.toString(DoubleBuffer.array())); 
  
        System.out.println("Position: " + DoubleBuffer.position()); 
  
        System.out.println("limit: " + DoubleBuffer.limit()); 
  
        // putting the value in compacted Doublebuffer 
        DoubleBuffer.put(9.61F); 
  
        // print the DoubleBuffer 
        System.out.println("\nUpdated Compacted DoubleBuffer: "
                           + Arrays.toString(DoubleBuffer.array())); 
        System.out.println("Position: " + DoubleBuffer.position()); 
        System.out.println("limit: " + DoubleBuffer.limit()); 
    } 
} 

Output:

Original DoubleBuffer: [8.5600004196167, 9.609999656677246, 9.609999656677246, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
Position: 3
limit: 10

Compacted DoubleBuffer: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
Position: 7
limit: 10

Updated Compacted DoubleBuffer: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 9.609999656677246, 0.0, 0.0]
Position: 8
limit: 10

Examples 2: To show ReadOnlyBufferException

// 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 DoubleBuffer 
        int capacity = 10; 
  
        // Creating the DoubleBuffer 
        try { 
  
            // creating object of DoubleBuffer 
            // and allocating size capacity 
            DoubleBuffer db = DoubleBuffer.allocate(capacity); 
  
            // putting the value in Doublebuffer 
            db.put(8.56F); 
            db.put(9.61F); 
            db.put(9.61F); 
            db.rewind(); 
  
            // Creating a read-only copy of DoubleBuffer 
            // using asReadOnlyBuffer() method 
            DoubleBuffer db1 = db.asReadOnlyBuffer(); 
  
            // print the ReadOnlyBuffer 
            System.out.print("ReadOnlyBuffer DoubleBuffer: "); 
            while (db1.hasRemaining()) 
                System.out.print(db1.get() + ", "); 
            System.out.println(""); 
  
            // print the Position of DoubleBuffer db 
            System.out.println("\nPosition: " + db.position()); 
  
            // print the Limit of DoubleBuffer db 
            System.out.println("\nlimit: " + db.limit()); 
  
            // Creating a compacted  DoubleBuffer of same ReadOnlyBuffer 
            // using compact() method 
            System.out.println("\nTrying to compact the ReadOnlyBuffer db1"); 
            DoubleBuffer DoubleBuffer = db1.compact(); 
        } 
  
        catch (IllegalArgumentException e) { 
  
            System.out.println("Exception throws " + e); 
        } 
  
        catch (ReadOnlyBufferException e) { 
  
            System.out.println("Exception throws " + e); 
        } 
    } 
} 

Output:

ReadOnlyBuffer DoubleBuffer: 8.5600004196167, 9.609999656677246, 9.609999656677246, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 

Position: 0

limit: 10

Trying to compact the ReadOnlyBuffer db1
Exception throws java.nio.ReadOnlyBufferException