Java 中的字节缓冲区分配直接()方法，示例
原文:https://www . geeksforgeeks . org/bytebuffer-allocatedirect-method-in-Java-with-examples/
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，其标记将是未定义的，并且其每个元素将被初始化为零。它是否有一个后备数组是未知的。
该方法比 allocate()方法快 25%-75%。
语法:
public static ByteBuffer allocateDirect(int capacity)
参数:该方法以容量字节为参数。
返回值:该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。
以下是说明 allocateDirect()方法的示例:
实施例 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);
}
}
}
Output:
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);
}
}
}
Output:
Trying to allocate negative value in ByteBuffer
Exception thrown : java.lang.IllegalArgumentException: Negative capacity: -4
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