如何将具有多个参数的对象的单个参数添加到该对象的数组列表中的字符串？

Question

我正在尝试重写 toString() 以打印名称。我使用对象员工数组列表中每个员工的 getNm() 。员工有参数（工资、nm、工作时间、加班时间）
我已将我关注的代码加粗。

public class Main {
    public static void main(String[] args){
        workers workerlist = new workers();
        workerlist.setNumberEmployees();
        workerlist.instantiateEmployees();
        System.out.println(workerlist.toString());
    }
}

public class Employees extends workers{
    public double pay;
    public String nm;
    public double hours;
    public double overtime;

    public Employees(double pay, String nm, double hoursWorked, double overtimeHours){
    }

        public double getPay(){
            return pay;
        }

        public void setPay(double pay){
        }

        public String getNm(){
            return nm;
        }

        public void setNm(String nm){
        }

        public double getHours(){
            return hours;
        }

        public void setHours(double hours){
        }

        public double getOvertime(){
            return overtime;
        }

        public void setOvertime(double overtime){
        }

    }

  import java.util.ArrayList;
import java.util.Scanner;

public class workers{
    public int employeenumber;
    public String nm;
    ArrayList<Employees> workerList = new ArrayList<Employees>();
    Scanner input = new Scanner(System.in);

    public void setNumberEmployees(){
        System.out.println("How many employees do you have?");
        employeenumber = input.nextInt();
    }

    public int getNumberEmployees(){
        return employeenumber;
    }

    public void instantiateEmployees(){
        for(int i=1; i<=employeenumber; i++){
            workerList.add(new Employees(0.0, "nm", 0.0, 0.0));
        }
    }


    public String toString(){
        String st = "";
        for(int i=0; i<employeenumber; i++){
            **st += workerList.toString();**
// ".toString() is there to test the setting of parameters, I am interested in replacing this part.
        }

        return st;
    }

}

预期输出 [员工 1 的姓名，员工 2 的姓名，...员工 n 的姓名]

Answer 1

我认为下面的代码会给出你预期的结果。

public class Main {
    public static void main(String[] args) {
        workers workerlist = new workers();
        workerlist.setNumberEmployees();
        workerlist.instantiateEmployees();
        System.out.println(workerlist.toString()); //call toString to take workerlist
    }
}

重写Employees toString方法，不要忘记在构造函数中更新nm参数

public class Employees extends workers {
    public double pay;
    public String nm;
    public double hours;
    public double overtime;

    public Employees(double pay, String nm, double hoursWorked, double overtimeHours) {
        this.nm = nm; //do not forget set value
    }

    public double getPay() {
        return pay;
    }

    public void setPay(double pay) {
    }

    public String getNm() {
        return nm;
    }

    public void setNm(String nm) {
    }

    public double getHours() {
        return hours;
    }

    public void setHours(double hours) {
    }

    public double getOvertime() {
        return overtime;
    }

    public void setOvertime(double overtime) {
    }

    @Override
    public String toString() {
        return getNm(); //Employees toString method will return nm
    }

}

重写toString方法并调用arraylist的toString方法。

public class workers {
    public int employeenumber;
    public String nm;
    ArrayList<Employees> workerList = new ArrayList<Employees>();
    Scanner input = new Scanner(System.in);

    public void setNumberEmployees() {
        System.out.println("How many employees do you have?");
        employeenumber = input.nextInt();
    }

    public int getNumberEmployees() {
        return employeenumber;
    }

    public void instantiateEmployees() {
        for (int i = 1; i <= employeenumber; i++) {
            workerList.add(new Employees(0.0, "nm", 0.0, 0.0));
        }
    }

    public String toString() {
        return workerList.toString(); //no need to iterate on arraylist, Arraylist.toString method will call each Employees toString method.
    }
}

Answer 2

Yusuf K. 和 Andrew Tobilko 已正确回答您的问题。只是给你一些提示来改进你的课程：

• 为什么你叫Employees，即使你的类可以代表一个雇员；所以我会改为 Employee。
• 为什么要定义两次 nm 字段？它在 Employees 类派生的 Workers 类中声明。

• setNumberEmployees() 方法不符合 JavaBeans 约定；它必须声明为

  public void setNumberEmployees(final String noEmployees) {
      employeenumber = noEmployees;
  }
  

  并且对 setNumberEmployees() 的调用应该在 ma​​in() 方法中作为

  public static void main(String[] args){
      workers workerlist = new workers();
      Scanner input = new Scanner(System.in);
      workerlist.setNumberEmployees(input.nextInt());
      workerlist.instantiateEmployees();
      System.out.println(workerlist.toString());
  }
  

• 最后，您说的是参数。它们实际上称为字段或实例变量。

Answer 3

public String toString(){
    String st = "";
    for(int i=0; i < employeenumber; i++)
        st += workerList.get(i).toString();

    return st;
}

但是这个解决方案并不是最好的。我建议你下一个：

public String toString(){
    StringBuilder builder = new StringBuilder();
    workerList.stream().map(Employees::toString).forEach(builder::append);

    return builder.toString();
}

当然，您必须在 Employees 类中覆盖 toString()。例如，

@Override public String toString() {
    return new StringJoiner(", ")
                .add(Double.toString(pay))
                .add(nm)
                .add(Double.toString(hours))
                .add(Double.toString(overtime))
            .toString();
}