Java Guava BigIntegerMath ceilingPowerOfTwo()用法及代碼示例

Guava BigIntegerMath類的ceilingPowerOfTwo(BigInteger x)方法返回大於或等於x的2的最小冪。這等效於BigInteger.valueOf(2).pow(log2(x，CEILING))。

用法:

public static BigInteger 
    ceilingPowerOfTwo(BigInteger x)

參數：此方法將數字x作為其最大冪為2的參數。

返回值：此方法返回給定數字x的2的上限功率。

異常：如果x <= 0，則此方法引發IllegalArgumentException。

以下示例說明了BifIntegerMath.ceilingPowerOfTwo()方法：

範例1：

// Java code to show implementation of 
// ceilingPowerOfTwo(BigInteger x) method 
// of Guava's BigIntegerMath class 
  
import java.math.*; 
import com.google.common.math.BigIntegerMath; 
  
class GFG { 
  
    // Driver code 
    public static void main(String args[]) 
    { 
        BigInteger n1 = BigInteger.valueOf(25); 
  
        // Using ceilingPowerOfTwo(BigInteger x) method of 
        // Guava's BigIntegerMath class 
        BigInteger ans = BigIntegerMath.ceilingPowerOfTwo(n1); 
  
        System.out.println("Smallest power of 2 greater "
                           + "than or equal to "
                           + n1 + " is:" + ans); 
  
        BigInteger n2 = BigInteger.valueOf(65); 
  
        // Using ceilingPowerOfTwo(BigInteger x) method of 
        // Guava's BigIntegerMath class 
        BigInteger ans1 = BigIntegerMath.ceilingPowerOfTwo(n2); 
  
        System.out.println("Smallest power of 2 greater "
                           + "than or equal to "
                           + n2 + " is:" + ans1); 
    } 
}

輸出：

Smallest power of 2 greater than or equal to 25 is:32
Smallest power of 2 greater than or equal to 65 is:128

範例2：

// Java code to show implementation of 
// ceilingPowerOfTwo(BigInteger x) method 
// of Guava's BigIntegerMath class 
  
import java.math.*; 
import com.google.common.math.BigIntegerMath; 
  
class GFG { 
  
    // Driver code 
    public static void main(String args[]) 
    { 
  
        try { 
  
            BigInteger n = BigInteger.valueOf(0); 
  
            // Using ceilingPowerOfTwo(BigInteger x) method of 
            // Guava's BigIntegerMath class 
            // This should raise "IllegalArgumentException" 
            // as n is <= 0 
            BigInteger ans = BigIntegerMath.ceilingPowerOfTwo(n); 
  
            System.out.println("Smallest power of 2 greater "
                               + "than or equal to n is:" + ans); 
        } 
        catch (Exception e) { 
            System.out.println("Exception:" + e); 
        } 
    } 
}

輸出：

Exception:java.lang.IllegalArgumentException:x (0) must be > 0

參考： https://google.github.io/guava/releases/21.0/api/docs/com/google/common/math/BigIntegerMath.html#ceilingPowerOfTwo-java.math.BigInteger-

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