Java中的 ByteBuffer allocateDirect() 方法及示例

使用Java.nio.ByteBuffer类的allocateDirect()方法分配一个新的直接字节缓冲区。

新缓冲区的位置将为零，其限制将是其容量，其标记将未定义，并且其每个元素将被初始化为零。它是否有一个支持数组是未指定的。

此方法比 allocate() 方法快 25%-75%。

句法：

public static ByteBuffer allocateDirect(int capacity)

参数：此方法将容量（以字节为单位）作为参数。

返回值：此方法返回新的字节缓冲区。

异常：此方法抛出IllegalArgumentException ，如果容量为负整数。

下面是说明 allocateDirect() 方法的示例：

示例 1：

// Java program to demonstrate
// allocateDirect() 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.allocateDirect(capacity);
  
            // creating byte array of size capacity
            byte[] value = { 20, 30, 40, 50 };
  
            // wrap the byte array into ByteBuffer
            bb = ByteBuffer.wrap(value);
  
            // print the ByteBuffer
            System.out.println("Direct ByteBuffer:  "
                               + Arrays.toString(bb.array()));
  
            // print the state of the buffer
            System.out.print("\nState of the ByteBuffer : ");
            System.out.println(bb.toString());
        }
  
        catch (IllegalArgumentException e) {
            System.out.println("Exception thrown : " + e);
        }
  
        catch (ReadOnlyBufferException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

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

State of the ByteBuffer : java.nio.HeapByteBuffer[pos=0 lim=4 cap=4]

示例 2：显示 IllegalArgumentException

// Java program to demonstrate
// allocateDirect() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // Declaring the capacity
        // with negative value
        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.allocateDirect(capacity);
  
            // creating byte array of size capacity
            byte[] value = { 20, 30, 40, 50 };
  
            // wrap the byte array into ByteBuffer
            bb = ByteBuffer.wrap(value);
  
            // print the ByteBuffer
            System.out.println("Direct ByteBuffer:  "
                               + Arrays.toString(bb.array()));
  
            // print the state of the buffer
            System.out.print("\nState of the ByteBuffer : ");
            System.out.println(bb.toString());
        }
  
        catch (IllegalArgumentException e) {
            System.out.println("Exception thrown : " + e);
        }
  
        catch (ReadOnlyBufferException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Trying to allocate negative value in ByteBuffer
Exception thrown : java.lang.IllegalArgumentException: Negative capacity: -4