調用過濾器內的方法時出現Java Streams錯誤

Question

我有兩個班級如下

    package academy.learnprogramming;
    
        public class Employee {
            int empId;
            int salary;
            String name;
            String designation;
        
            Employee(int empId, String name, String designation, int salary){
                this.empId = empId;
                this.name = name;
                this.designation = designation;
                this.salary = salary;
            }
        
            public String toString(){
                return "ID = "+empId + ", Name = "+name+", Designation = "+designation+", Salary = "+salary;
            }
            public String filterData(){
                if(empId == 111 && salary > 1000){
                    return "ID = "+empId + ", Name = "+name+", Designation = "+designation+", Salary = "+salary;
                }
                return  "";
            }
        }

package academy.learnprogramming;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class Main {
    public static List<Employee> employeeList = new ArrayList<Employee>();

    public static void main(String[] args) {
        Employee employee1 = new Employee(111,"Niranjan","SSE",10000);
        Employee employee2 = new Employee(112,"Niramal","SSE-1",10001);
        Employee employee3 = new Employee(113,"Nijaguna","SSE-2",10);


        employeeList.add(employee1);
        employeeList.add(employee2);
        employeeList.add(employee3);
        /*for (Employee employee: employeeList){
            System.out.println(employee.toString());
        }*/
        employeeList.stream().forEach(System.out::println);
        System.out.println("****");
        //employeeList.stream().filter(employee -> employee.salary > 10000 ).forEach(System.out::println);
        employeeList.stream().filter(Employee::filterData).map(employee->employee).collect(Collectors.toList());
        System.out.println("*******Sorted list*******");
    }
}

我在下面的行中收到錯誤，說方法參考中的返回類型錯誤：無法將 java.lang.String 轉換為布爾值

employeeList.stream().filter(Employee::filterData).map(employee->employee).collect(Collectors.toList());

有人可以幫忙嗎？ 學習java概念

如果有人幫助同樣會很有幫助

Answer 1

Stream#filter 期望流類型中的函數為布爾值，並將刪除該函數返回 false 的任何元素。 Employee#filterData 方法返回一個字符串，因此它不能作為過濾依據的函數。 相反，您需要一個返回布爾值的方法：如果流應該保留該員工，則為 true，如果不應該保留，則為 false。