Java ByteBuffer allocate()方法及示例

java.nio.ByteBuffer 类的 allocate() 方法是用来分配一个新的字节缓冲区。

新缓冲区的位置将是零，它的极限是它的容量，它的标记将是未定义的，它的每个元素将被初始化为零。它将有一个支持数组，它的数组偏移量将为零。

语法:

public static ByteBuffer allocate(int capacity)

参数： 该方法以容量为参数，单位为字节。

返回值： 该方法返回新的字节缓冲区。

抛出： 此方法抛出 IllegalArgumentException ，如果容量是一个负整数。

下面是一些例子来说明allocate()方法。

例子 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");
        }
    }
}

输出。

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

例子 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);
        }
    }
}

输出。

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