Java中的 ByteBuffer allocate() 方法及示例

Java.nio.ByteBuffer类的allocate()方法用于分配一个新的字节缓冲区。

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。它将有一个支持数组，并且它的数组偏移量为零。

句法 ：

public static ByteBuffer allocate(int capacity)

参数：此方法以容量为参数，以字节为单位。

返回值：此方法返回新的字节缓冲区。

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

下面是说明 allocate() 方法的示例：

示例 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]

示例 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