Java 中的 BitSet previousClearBit()方法
原文:https://www . geesforgeks . org/bitset-previousclearbit-method-in-Java/
BitSet 是 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 | Set 1
bitset . previousclearbit() 此方法用于查找作为参数传递的索引上或之前出现的假位。此方法返回发生在指定起始索引上或之前的设置为 false 的最近位的索引。如果不存在这样的位，或者如果给定-1 作为起始索引，则返回-1。
语法:
public int previousClearBit(int fromIndex)
参数:该方法取 fromIndex 作为开始检查的索引(含)。
返回值:该方法返回前一个清零位的索引，如果没有该位则返回-1
异常:如果指定的索引小于-1，该方法抛出indexout of boundsexception。
下面的程序举例说明了 previousCleatBit()方法:
程序 1:
// 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));
}
}
Output:
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 异常:
// 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);
}
}
}
Output:
bs1 : {0, 1, 2, 4}
Exception when index less than -1 is passed as parameter : java.lang.IndexOutOfBoundsException: fromIndex < -1: -2
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