如何用 java 中的流替换 for 循环

Question

class Checker{
        
    void CheckingNameFromDeptCode(LinkedList<Employee1> empObj, String deptID) 
    {
            for (int i = 0; i < empObj.size(); i++) {
                if (empObj.get(i).getDeptID().equals(deptID)) {
                    System.out.println(empObj.get(i).getEmpName());
                }
            }
    }
}

这是我创建的方法，用于检查输入的部门列表中的员工。但是有人告诉我在 java 8 中使用 streams/lambda 进行迭代，而不是我使用的好旧的 for 循环。

下面是主要方法

import java.util.*;
public class Manager{

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        LinkedList<Employee1> employeeObj = new LinkedList<Employee1>();
        Checker empBusObj = new Checker();
        
        employeeObj.add(new Employee1("Souvik", "D1", "Development", "L1", "Kolkata"));
        employeeObj.add(new Employee1("Anirban", "D2", "HR", "L2", "Bangalore"));
        employeeObj.add(new Employee1("Joydeep", "D3", "Design", "L3", "Delhi"));
        employeeObj.add(new Employee1("Rakesh", "D2", "HR", "L4", "Pune"));
        System.out.print("Enter the choices : ");
        int ch = sc.nextInt();
        String deptInput; 
        String locInput;
        switch (ch) 
        {
            case 1:
            System.out.print("Enter the department code : ");
            deptInput = sc.next();
            deptInput = deptInput.toUpperCase();
            empBusObj.CheckingNameFromDeptCode(employeeObj, deptInput); 
            break;

Answer 1

使用流代码将如下所示

empObj.stream().filter(obj -> {
    return obj.getDeptID().equals(deptID);
}).forEach(obj -> {
    System.out.println(obj.getEmpName());
});

或者parallelStream来一个并发处理：

empObj.parallelStream().filter(obj -> {
    return obj.getDeptID().equals(deptID);
}).forEach(obj -> {
    System.out.println(obj.getEmpName());
});

Answer 2

你可以像这样用 Stream api:

   void CheckingNameFromDeptCode(LinkedList<Employee1> empObj, String deptID) 
    {
       empObj.stream().filter(employer -> 
           employer.getId().equals(deptID)).forEach(employer -> 
               System.out.println(employer.getEmpName()));
    }

Answer 3

如果您的问题只是“我需要使用 streams/lambdas”，下面是一个使用流的示例：

public static void main(String[] args) {
    String deptID = "DPT-01";
    List<Employee> employees = new ArrayList<>();
   //                          UUID      DEPTID    NAME
    employees.add(new Employee("UID-01", "DPT-01", "Foo"));
    employees.add(new Employee("UID-02", "DPT-02", "Bar"));
    employees.add(new Employee("UID-03", "DPT-01", "AnEmployee"));
    employees.add(new Employee("UID-04", "DPT-03", "AnotherEmployee"));

    List<Employee> filtered = employees.stream().filter(emp -> emp.getDeptID().equals(deptID)).collect(Collectors.toList());
    filtered.forEach(System.out::println); // Here you can also use the double colon operator!
}

您可以在此处找到有关流的更多信息：https://www.baeldung.com/java-streams

关于这里的双冒号运算符：https://www.baeldung.com/java-8-double-colon-operator

编辑

有评论推荐使用Stream的forEach()方法，这里举个不收集元素的例子：

public static void main(String[] args) {
String deptID = "DPT-01";
    List<Employee> employees = new ArrayList<>();
   //                          UUID      DEPTID    NAME
    employees.add(new Employee("UID-01", "DPT-01", "Foo"));
    employees.add(new Employee("UID-02", "DPT-02", "Bar"));
    employees.add(new Employee("UID-03", "DPT-01", "AnEmployee"));
    employees.add(new Employee("UID-04", "DPT-03", "AnotherEmployee"));
    employees
        .stream()
        .filter(emp -> emp.getDeptID().equals(deptID))
        .forEach(emp -> System.out.println(emp.getEmpName());
}

给你：没有 double colon operator，没有 Collectors，没有 toString()。请记住，这只是一个示例。

顺便说一句，这是我使用的 Employee class：

public class Employee {

private String userID;
private String deptID;
private String empName;

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

public String getUserID() {
    return userID;
}

public void setUserID(String userID) {
    this.userID = userID;
}

public String getDeptID() {
    return deptID;
}

public void setDeptID(String deptID) {
    this.deptID = deptID;
}

public String getEmpName() {
    return empName;
}

public void setEmpName(String empName) {
    this.empName= empName;
}

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    Employee employee = (Employee) o;
    return Objects.equals(empName, employee.empName) && Objects.equals(deptID, employee.deptID) && Objects.equals(userName, employee.userName);
}

@Override
public int hashCode() {
    return Objects.hash(empName, deptID, userName);
}

@Override
public String toString() {
    return "Employee{" +
            "empName='" + empName+ '\'' +
            ", deptID='" + deptID + '\'' +
            ", userName='" + userName + '\'' +
            '}';
}
}

如何用 java 中的流替换 for 循环

How to replace for loop with streams in java

java

iteration

java-8

java-stream

编辑