Java中的 BitSet previousClearBit() 方法

BitSet 是在Java.util 包中定义的一个类。它创建一个由布尔值表示的位数组。

先决条件： Java BitSet |设置 1

Bitset.previousClearBit()
此方法用于查找在作为参数传递的索引上或之前出现的错误位。此方法返回在指定起始索引上或之前设置为 false 的最近位的索引。如果不存在这样的位，或者如果给出 -1 作为起始索引，则返回 -1。

句法：

public int previousClearBit(int fromIndex)

参数：此方法采用fromIndex ，它是开始检查的索引（包括）。

返回值：此方法返回前一个清除位的索引，如果没有该位，则返回-1

异常：如果指定的索引小于 -1，此方法将抛出IndexOutOfBoundsException 。

下面的程序说明了 previousCleatBit() 方法：

方案一：

// Java program illustrating Bitset
// previousClearBit() function
  
import java.util.*;
public class GFG
{
    public static void main(String[] args)
    {
        // Constructors of BitSet class
        BitSet bs1 = new BitSet();
        BitSet bs2 = new BitSet();
        BitSet bs3 = new BitSet();
          
        /* assigning values to set1*/
        bs1.set(0);
        //bs1.set(1);
        bs1.set(2);
        bs1.set(4);
  
        // assign values to bs2
        bs2.set(4);
        bs2.set(6);
        bs2.set(5);
        bs2.set(1);
        bs2.set(2);
        bs2.set(3);
        bs2.set(12);
  
        // Printing the 2 Bitsets
        System.out.println("bs1 : " + bs1);
        System.out.println("bs2 : " + bs2);
        System.out.println("bs3 : " + bs3);
          
        // Performing previousClearBit() on bitsets
        System.out.println("Previous Clear Bit of bs1"
+ bs1.previousClearBit(0));
        System.out.println("Previous Clear Bit of bs2"
+ bs2.previousClearBit(5));
        System.out.println("Previous Clear Bit of bs3"
+ bs3.previousClearBit(3));
          
    }
} 

输出：

bs1 : {0, 2, 4}
bs2 : {1, 2, 3, 4, 5, 6, 12}
bs3 : {}
Previous Clear Bit of bs1-1
Previous Clear Bit of bs20
Previous Clear Bit of bs33

程序 2：显示 IndexOutOfBoundException：

// Java program illustrating Bitset
// previousClearBit() function.
  
import java.util.*;
public class GFG {
    public static void main(String[] args)
    {
        // Constructors of BitSet class
        BitSet bs1 = new BitSet();
  
        // assigning values to set1
        bs1.set(0);
        bs1.set(1);
        bs1.set(2);
        bs1.set(4);
  
        // Printing the Bitset
        System.out.println("bs1 : " + bs1);
  
        try {
            // Passing -2 as parameter
            System.out.println(bs1.previousClearBit(-2));
        }
        catch (Exception e) {
            System.out.println("Exception when "
                               + "index less than -1 is passed "
                               + "as parameter : " + e);
        }
    }
}

输出：

bs1 : {0, 1, 2, 4}
Exception when index less than -1 is passed as parameter : java.lang.IndexOutOfBoundsException: fromIndex < -1: -2