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题目

(1)有如下代码：

List<String> list = new ArrayList<>();

list.add("a");

list.add("a"); list.add("a"); list.add("b"); list.add("b"); list.add("c"); list.add("d"); list.add("d"); list.add("d"); list.add("d"); list.add("d");

System.out.println(frequency(list, "a"));    // 3

System.out.println(frequency(list, "b"));    // 2 System.out.println(frequency(list, "c"));    // 1 System.out.println(frequency(list, "d"));    // 5 System.out.println(frequency(list, "xxx"));    // 0 (2)定义方法统计集合中指定元素出现的次数，如"a" 3,"b" 2,"c" 1

代码实现

public class demo {		public static int frequency(List
   
     list,String string) {				int count = 0;		for(String s:list) {			if(string.equals(s)) {				count++;			}		}				return count;	}		public static void main(String[] args) {			List
    
      list = new ArrayList<>();				list.add("a");		list.add("a");		list.add("a");		list.add("b");		list.add("b");		list.add("c");		list.add("d");		list.add("d");		list.add("d");		list.add("d");		list.add("d");		System.out.println(frequency(list, "a"));	// 3		System.out.println(frequency(list, "b"));	// 2		System.out.println(frequency(list, "c"));	// 1		System.out.println(frequency(list, "d"));	// 5		System.out.println(frequency(list, "xxx"));	// 0			}}
    
   

 

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