Java 简明教程

Java BitSet Class

Introduction

Java BitSet 类创建了一个特殊类型，可保存位值。BitSet 数组可以根据需要增加大小。这使其类似于位向量。这是一个旧类，但是它已经过 Java 2 1.4 版的完全重构。

The Java BitSet class creates a special type of array that holds bit values. The BitSet array can increase in size as needed. This makes it similar to a vector of bits. This is a legacy class but it has been completely re-engineered in Java 2, version 1.4.

Java BitSet 类实现了一个根据需要增长的位向量。以下是有关 BitSet 的重要要点——

The Java BitSet class implements a vector of bits that grows as needed.Following are the important points about BitSet −

  1. A BitSet is not safe for multithreaded use without external synchronization.

  2. All bits in the set initially have the value false.

  3. Passing a null parameter to any of the methods in a BitSet will result in a NullPointerException.

Class declaration

以下是 java.util.BitSet 类的声明——

Following is the declaration for java.util.BitSet class −

public class BitSet
   extends Object
   implements Cloneable, Serializable

Class constructors

Class methods

Methods inherited

此类从以下类中继承方法：

This class inherits methods from the following classes −

  1. java.util.Object

Creating a BitSet and Performing Operations on BitSets Example

以下程序展示了位集数据结构支持的几种方法 −

The following program illustrates several of the methods supported by BitSet data structure −

import java.util.BitSet;
public class BitSetDemo {

  public static void main(String args[]) {
      BitSet bits1 = new BitSet(16);
      BitSet bits2 = new BitSet(16);

      // set some bits
      for(int i = 0; i < 16; i++) {
         if((i % 2) == 0) bits1.set(i);
         if((i % 5) != 0) bits2.set(i);
      }

      System.out.println("Initial pattern in bits1: ");
      System.out.println(bits1);
      System.out.println("\nInitial pattern in bits2: ");
      System.out.println(bits2);

      // AND bits
      bits2.and(bits1);
      System.out.println("\nbits2 AND bits1: ");
      System.out.println(bits2);

      // OR bits
      bits2.or(bits1);
      System.out.println("\nbits2 OR bits1: ");
      System.out.println(bits2);

      // XOR bits
      bits2.xor(bits1);
      System.out.println("\nbits2 XOR bits1: ");
      System.out.println(bits2);
   }
}

这会产生以下结果 −

This will produce the following result −

Output

Initial pattern in bits1:
{0, 2, 4, 6, 8, 10, 12, 14}

Initial pattern in bits2:
{1, 2, 3, 4, 6, 7, 8, 9, 11, 12, 13, 14}

bits2 AND bits1:
{2, 4, 6, 8, 12, 14}

bits2 OR bits1:
{0, 2, 4, 6, 8, 10, 12, 14}

bits2 XOR bits1:
{}