Java中的Java .util.Collections.frequency() 和示例

Java.util.Collections.frequency()方法存在于Java.util.Collections 类中。它用于获取指定集合列表中存在的元素的频率。更正式地说，它返回集合中元素 e 的数量。

句法

public static int frequency(Collection c, Object o)
Parameters : 
c - the collection in which to determine the frequency of o
o - the object whose frequency is to be determined
Returns :
Returns the number of elements in the specified collection 
equal to the specified object.
Throws:
NullPointerException - if c is null

// Java program to demonstrate working of 
// java.utils.Collections.frequency()
  
import java.util.*;
   
public class FrequencyDemo
{
    public static void main(String[] args)
    {
        // Let us create a list of strings
        List  mylist = new ArrayList();
        mylist.add("practice");
        mylist.add("code");
        mylist.add("code");
        mylist.add("quiz");
        mylist.add("geeksforgeeks");
   
        // Here we are using frequency() method
        // to get  frequency of element "code"
        int freq = Collections.frequency(mylist, "code");
   
        System.out.println(freq);
    }
}

输出：

2

如何在Java中快速获取数组中元素的频率？

Java中的数组类没有频率方法。但是我们也可以使用 Collections.frequency() 来获取数组中元素的频率。

// Java program to get frequency of an element 
//  with java.utils.Collections.frequency()
  
import java.util.*;
   
public class FrequencyDemo
{
    public static void main(String[] args)
    {
        // Let us create an array of integers
        Integer arr[] = {10, 20, 20, 30, 20, 40, 50};
   
        // Please refer below post for details of asList()
        // https://www.geeksforgeeks.org/array-class-in-java/
        int freq = Collections.frequency(Arrays.asList(arr), 20);
   
        System.out.println(freq);
    }
}

输出：

3