toString（）如何在以下程序中使用Predicate

Question

任何人都可以解释一下toString（）函数如何使用这个谓词。我理解lambda表达式但是如何调用toString（）函数。

import java.util.function.*;
import java.util.*;
class Demo{
public static void main(String arv[]){
    HashSet <Employee> hs = new HashSet<>();
    hs.add(new Employee("A",40000,25,"CSE"));
    hs.add(new Employee("B",50000,26,"CSE"));
    hs.add(new Employee("C",54000,30,"ECEadsa"));
    hs.add(new Employee("D",45000,25,"ECE"));
    hs.add(new Employee("E",60000,32,"CSE"));
    Predicate <Employee> emp = t -> t.salary > 50000;
    Predicate <Employee> emp1 = emp.and( t -> t.department.length()>5);
    for(Employee e: hs)
    if (emp1.test(e))
    System.out.println(e);
                                     }
         }
class Employee{
   String name;
   double salary;
   int age;
   String department;
   Employee(String n, double s, int a, String d){
   name = n;
   salary = s;
   age = a;
   department = d;
              }
public String toString(){
   return " name = "+name+" salary = "+salary+" age = "+age+" department = "+department;
                        }
               }

输出：name = C salary = 54000.0 age = 30 department = ECEadsa

Answer 1

您已经添加了用于打印Employee的代码，当您打印任何对象时，如果存在，则为该类调用toString（）方法调用其他toString的方法

  for(Employee e: hs)
    if (emp1.test(e))
    System.out.println(e);
              }
         }

对于具有department.length（）> 5的打印逻辑System.out.println（e）的员工;叫做

Answer 2

在PrintStream类中，println（Object x）方法使用String.valueOf（x），它调用对象的toString（）。如果您没有覆盖toString（）方法，则可以使用Object类的默认实现。