Java 中的 ByteBuffer compact()方法，带示例
原文:https://www . geeksforgeeks . org/bytebuffer-compact-method-in-Java-with-examples/
java.nio.ByteBuffer 类的 compact() 方法用于压缩给定的缓冲区。 缓冲区当前位置与其限制之间的字节(如果有)被复制到缓冲区的开头。也就是说，索引 p =位置()的字节被复制到索引 0，索引 p + 1 的字节被复制到索引 1，以此类推，直到索引限制()–1 的字节被复制到索引 n =限制()–1–p。然后，缓冲区的位置被设置为 n+1，其限制被设置为其容量。如果定义了标记，则会将其丢弃。 缓冲区的位置被设置为复制的字节数，而不是零，这样调用该方法后可以立即调用另一个相对 put 方法。 从缓冲区写入数据后调用此方法，以防写入不完整。 语法:
public abstract ByteBuffer compact()
返回值:该方法返回与该缓冲区内容相同的新字节缓冲区。 异常:如果这个缓冲区是只读的，这个方法抛出 ReadOnlyBufferException。 以下程序说明了紧凑()方法: 例 1:
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate
// compact() method
import java.nio.*;
import java.util.*;
public class GFG {
public static void main(String[] args)
{
// Declaring the capacity of the ByteBuffer
int capacity = 7;
// Creating the ByteBuffer
// 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);
// print the ByteBuffer
System.out.println("Original ByteBuffer: "
+ Arrays.toString(bb.array()));
System.out.println("Position: " + bb.position());
System.out.println("limit: " + bb.limit());
// Creating a compacted ByteBuffer of same ByteBuffer
// using compact() method
ByteBuffer cbb = bb.compact();
// print the ByteBuffer
System.out.println("\nCompacted ByteBuffer: "
+ Arrays.toString(cbb.array()));
System.out.println("Position: " + cbb.position());
System.out.println("limit: " + cbb.limit());
// putting the int to byte typecast value in compacted ByteBuffer
cbb.put((byte)50);
// print the ByteBuffer
System.out.println("\nUpdated Compacted ByteBuffer: "
+ Arrays.toString(cbb.array()));
System.out.println("Position: " + cbb.position());
System.out.println("limit: " + cbb.limit());
}
}
Output:
Original ByteBuffer: [20, 30, 40, 0, 0, 0, 0]
Position: 3
limit: 7
Compacted ByteBuffer: [0, 0, 0, 0, 0, 0, 0]
Position: 4
limit: 7
Updated Compacted ByteBuffer: [0, 0, 0, 0, 50, 0, 0]
Position: 5
limit: 7
例 2:
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate
// compact() method
import java.nio.*;
import java.util.*;
public class GFG {
public static void main(String[] args)
{
// Declaring the capacity of the ByteBuffer
int capacity = 5;
// 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.rewind();
// Creating a read-only copy of ByteBuffer
// using asReadOnlyBuffer() method
ByteBuffer bb1 = bb.asReadOnlyBuffer();
// print the ReadOnlyBuffer
System.out.print("ReadOnlyBuffer ByteBuffer: ");
while (bb1.hasRemaining())
System.out.print(bb1.get() + ", ");
System.out.println("");
// print the Position of ByteBuffer bb
System.out.println("\nPosition: " + bb.position());
// print the Limit of ByteBuffer bb
System.out.println("\nlimit: " + bb.limit());
// Creating a compacted ByteBuffer of same ReadOnlyBuffer
// using compact() method
System.out.println("\nTrying to compact the ReadOnlyBuffer bb1");
ByteBuffer rbb = bb1.compact();
}
catch (IllegalArgumentException e) {
System.out.println("Exception throws " + e);
}
catch (ReadOnlyBufferException e) {
System.out.println("Exception throws " + e);
}
}
}
Output:
ReadOnlyBuffer ByteBuffer: 20, 30, 40, 0, 0,
Position: 0
limit: 5
Trying to compact the ReadOnlyBuffer bb1
Exception throws java.nio.ReadOnlyBufferException
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