Java 中的 ByteBuffer arrayOffset()方法，带示例
原文:https://www . geeksforgeeks . org/bytebuffer-arrayoffset-method-in-Java-with-examples/
java.nio.ByteBuffer 类的 arrayOffset() 方法用于返回给定缓冲区的后备数组中缓冲区第一个元素的偏移量。
如果这个缓冲区由一个数组支持，那么缓冲区位置 p 对应于数组索引 p + arrayOffset()。
在调用此方法之前，调用 hasArray 方法，以确保此缓冲区具有可访问的后备数组。
语法:
public final int arrayOffset()
返回值:该方法返回该缓冲区数组中缓冲区第一个元素的偏移量
异常::如果此缓冲区由数组支持但为只读，则此方法将引发readonlybufferenexception，。
以下是说明 arrayOffset()方法的示例:
例 1:
// Java program to demonstrate
// arrayOffset() 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
bb.put((byte)20);
bb.put((byte)30);
bb.put((byte)40);
bb.put((byte)50);
bb.rewind();
// print the ByteBuffer
System.out.println("ByteBuffer: "
+ Arrays.toString(bb.array()));
// print the arrayOffset
System.out.println("arrayOffset: "
+ bb.arrayOffset());
}
catch (IllegalArgumentException e) {
System.out.println("IllegalArgumentException catched");
}
catch (ReadOnlyBufferException e) {
System.out.println("Exception throws" + e);
}
}
}
Output:
ByteBuffer: [20, 30, 40, 50]
arrayOffset: 0
例 2:
// Java program to demonstrate
// arrayOffset() method
import java.nio.*;
import java.util.*;
public class GFG {
public static void main(String[] args)
{
// Declaring the capacity of the ByteBuffer
int capacity = 3;
// Creating the ByteBuffer
try {
// creating object of ByteBuffer
// and allocating size capacity
ByteBuffer bb = ByteBuffer.allocate(capacity);
// putting the value in ByteBuffer
bb.put((byte)20);
bb.put((byte)30);
bb.put((byte)40);
bb.rewind();
// Creating a read-only copy of ByteBuffer
// using asReadOnlyBuffer() method
ByteBuffer bb1 = bb.asReadOnlyBuffer();
// print the ByteBuffer
System.out.print("Read only buffer : ");
while (bb1.hasRemaining())
System.out.print(bb1.get() + ", ");
// next line
System.out.println("");
// print the arrayOffset
System.out.println("\nTry to print the array offset"
+ " of read only buffer");
System.out.println("arrayOffset: " + bb1.arrayOffset());
}
catch (IllegalArgumentException e) {
System.out.println("Exception throws: " + e);
}
catch (ReadOnlyBufferException e) {
System.out.println("Exception throws: " + e);
}
}
}
Output:
Read only buffer : 20, 30, 40,
Try to print the array offset of read only buffer
Exception throws: java.nio.ReadOnlyBufferException
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