Java DoubleBuffer compact()方法及实例

java.nio.DoubleBuffer 类的 compact() 方法用于压缩给定的缓冲区。

缓冲区的当前位置和极限之间的值被复制到缓冲区的开头。然后，缓冲区的位置被设置为n+1，其极限被设置为其容量。缓冲区的位置被设置为复制的浮点数。

语法:

public abstract DoubleBuffer compact()

返回值： 该方法返回 新的DoubleBuffer ，其内容与此缓冲区相同。

异常： 如果这个缓冲区是只读的，这个方法会抛出 ReadOnlyBufferException 。

下面的程序说明了 compact() 方法。

例子 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());
    }
}

输出:

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

示例2： 显示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);
        }
    }
}

输出:

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