Java 中的缓冲区 arrayOffset()方法，带示例
原文:https://www . geesforgeks . org/buffer-arrayoffset-method-in-Java-with-examples/
java.nio.Buffer 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 abstract 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);
// Typecasting ByteBuffer into Buffer
Buffer buffer = (Buffer)bb;
// offset within this buffer's array
// of the first element of the buffer
// using arrayOffset() method
int offset = buffer.arrayOffset();
// print the array
System.out.println("arrayOffset is : "
+ offset);
}
catch (ReadOnlyBufferException e) {
System.out.println("buffer is backed by an "
+ "array but is read-only");
System.out.println("Exception throws: " + e);
}
}
}
输出:
arrayOffset is : 0
例 2: 为 readonly buffer exception
// 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);
// Creating a read-only copy of ByteBuffer
// using asReadOnlyBuffer() method
ByteBuffer bb1 = bb.asReadOnlyBuffer();
// Typecasting read-only ByteBuffer
// into read-only Buffer
Buffer buffer = (Buffer)bb1;
// offset within this buffer's array
// of the first element of the buffer
// using arrayOffset() method
int offset = buffer.arrayOffset();
// print the array
System.out.println("arrayOffset is : "
+ offset);
}
catch (ReadOnlyBufferException e) {
System.out.println("buffer is backed by "
+ "an array but is read-only");
System.out.println("Exception throws: " + e);
}
}
}
T5】输出:
buffer is backed by an array but is read-only
Exception throws: java.nio.ReadOnlyBufferException
参考:https://docs . Oracle . com/javase/9/docs/API/Java/nio/buffer . html # arrayOffset–
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