java - 使用 'Collections.frequency' 获取给定一个值的实例计数

Question

为了简化我正在做的事情，让我们使用 learnfromexamples.com 中的示例我修改了一些位。

package test;
import java.util.StringTokenizer;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;


class Employee {
        private String empno;
        private String empName;

        public Employee(String empno, String empName ) {
            this.empno = empno;
            this.empName = empName;
        }

        public String getEmpno() {
            return empno;
        }

        public void setEmpno(String empno) {
            this.empno = empno;
        }

        public String getEmpName() {
            return empName;
        }

        public void setEmpName(String empName) {
            this.empName = empName;
        }
        @Override
        public String toString() {
            return "Empno is "+ empno + " Empname is " + empName;
        }
        public Employee() {
            // TODO Auto-generated constructor stub
        }

        @Override
        public boolean equals(Object arg0) {
            // TODO Auto-generated method stub
            boolean flag = false;
            Employee employee = (Employee) arg0;
            if(null!= employee && employee.getEmpName().equalsIgnoreCase(empName) && employee.getEmpno().equalsIgnoreCase(empno)){
                flag = true;
            }
            return flag;
        }

    }


public class Test  {
    public static void main(String[] args) {

        List<Employee> empList = new ArrayList<Employee>();
        empList.add(new Employee("001", "Shidhar"));
        empList.add(new Employee("002", "Pathy"));
        empList.add(new Employee("003", "Sahana"));
        empList.add(new Employee("003", "Sahana"));
        empList.add(new Employee("004", "Sahana"));
        empList.add(new Employee("003", "Sahana"));

        //Get the occurrence of "new Employee("003", "Sahana")" from empLists
        //int sahanaCount = Collections.frequency(empList, new Employee("003"));
        //System.out.println("Count of sahana is : " +sahanaCount);

        Set<Employee> uniqueId = new HashSet<Employee>(empList);
        for (Employee emId : uniqueId) {
            System.out.println("The emp with id "+emId.getEmpno()+" was repeated: "
                    + Collections.frequency(empList, emId.getEmpName()));
        }

    }
}

是否可以使用Collections.Frequency来查找给定一个变量的频率，例如Collections.Frequency(empList,"Sahana"); 产生 4。

另一种选择是我可以使用 HashMap 来保持计数，但假设我对 Collections.Frequency 印象深刻，并尝试使用它。

Answer 1

不，考虑到您的 equals 实现，这是不可能的。在 Java-8 中，您可以使用 Stream API 代替 Collections.Frequency:

empList.stream().map(Employee::getEmpName).filter(emId.getEmpName()::equals).count();