Java中的缓冲区 mark() 方法及示例

Java.nio.Buffer 类的mark()方法用于设置这个缓冲区的标记在它的位置。
句法：

public Buffer mark()

返回值：此方法返回此缓冲区。
以下是说明 mark() 方法的示例：
示例 1：

Java

// Java program to demonstrate
// mark() method
 
import java.nio.*;
import java.util.*;
 
public class GFG {
 
    public static void main(String[] args)
    {
 
        try {
 
            byte[] barr = { 10, 20, 30, 40 };
 
            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.wrap(barr);
 
            // Typecasting ByteBuffer into Buffer
            Buffer bb1 = (Buffer)bb;
 
            // try to set the position at index 2
            bb1.position(2);
 
            // Set this buffer mark position
            // using mark() method
            bb1.mark();
 
            // try to set the position at index 4
            bb1.position(4);
 
            // display position
            System.out.println("position before reset: "
                               + bb1.position());
 
            // try to call reset() to restore
            // to the position we marked
            bb1.reset();
 
            // display position
            System.out.println("position after reset: "
                               + bb1.position());
        }
 
        catch (InvalidMarkException e) {
            System.out.println("new position is less than "
                               + "the position we marked before ");
            System.out.println("Exception throws: " + e);
        }
    }
}

输出：

position before reset: 4
position after reset: 2

示例 2：演示 InvalidMarkException

Java

// Java program to demonstrate
// mark() method
 
import java.nio.*;
import java.util.*;
 
public class GFG {
 
    public static void main(String[] args)
    {
 
        try {
 
            byte[] barr = { 10, 20, 30, 40 };
 
            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.wrap(barr);
 
            // Typecasting ByteBuffer into Buffer
            Buffer bb1 = (Buffer)bb;
 
            // try to set the position at index 2
            bb1.position(2);
 
            // Set this buffer mark position
            // using mark() method
            bb1.mark();
 
            // try to set the position at index 4
            bb1.position(1);
 
            // display position
            System.out.println("position before reset: "
                               + bb1.position());
 
            // try to call reset() to restore
            // to the position we marked
            bb1.reset();
 
            // display position
            System.out.println("position after reset: "
                               + bb1.position());
        }
 
        catch (InvalidMarkException e) {
            System.out.println("\new position is less than "
                               + "the position we marked before ");
            System.out.println("Exception throws: " + e);
        }
    }
}

输出：

position before reset: 1

new position is less than the position we marked before 
Exception throws: java.nio.InvalidMarkException

参考： https://docs.oracle.com/javase/9/docs/api/ Java/nio/Buffer.html#mark–