Question

这是一个较大项目的摘要。该项目旨在成为客户的客户经理+汇款的工作经理。在继续之前，我有一个我不明白的“小”问题。我想知道，为什么

System.out.println(myJobOrganizer.jobNumber); // in the Main.java

输出0，尽管我已将两个作业添加到jobList。在打印jobList本身时，它会打印出来

[[[customer1;adress1;accountBalance1];[customer2;adress2;accountBalance2];moneyToTransfer];[[customer3;adress3;accountBalance3];[customer4;address4;accountBalance4];moneyToTransfer2]]

jobOrganizer.java

import java.util.ArrayList;
import java.util.List;

public class jobOrganizer {

    private static final jobOrganizer myJobOrganizer = new jobOrganizer();

    public static jobOrganizer getMyJobOrganizer() {
        return myJobOrganizer;
    }

    private List<job> jobList = new ArrayList<job>();

    public int jobNumber = jobList.size();

    public void add_job(job newJob) {
        this.jobList.add(newJob);
    }

    public Iterable<job> all_jobs() {
        return this.jobList;
    }

    public static jobOrganizer getInstance() {
        return myJobOrganizer;
    }
}

job.java

    public class job implements Runnable {
    private customer kunde1;
    private customer kunde2;
    private Double transfer;

    public job(customer kunde1, customer kunde2, Double transfer) {
        this.kunde1 = kunde1;
        this.kunde2 = kunde2;
        this.transfer = transfer;
    }

    @Override
    public String toString() {
        return "[" + kunde1 + "; " + kunde2 + "; " + transfer + "]";
    }

    public void run() {
        System.out.println("Starting transfer");
        Double geber = this.kunde1.getAccountBalance();
        Double nehmer = this.kunde2.getAccountBalance();
        Double geberNeu = geber - this.transfer;
        this.kunde1.setAccountBalance(geberNeu);
        Double nehmerNeu = nehmer + this.transfer;
        this.kunde2.setAccountBalance(nehmerNeu);
        System.out.println("Transfer done");
    }
}

Main.java

public class Main {
    public static void main(String[] args) {
        customerOrganizer myCustomerOrganizer = new customerOrganizer();
        jobOrganizer myJobOrganizer = new jobOrganizer();

        customer mueller = new customer("Tim Mueller", "Strasse 1", 1077.00);
        customer john = new customer("John Doe", "Strasse 2", 503.00);
        customer meier = new customer("John Meier", "Strasse 3", 8500.50);
        customer wurst = new customer("Hans Wurst", "Strasse 4", 1000.00);

        myCustomerOrganizer.add_customer(mueller);
        myCustomerOrganizer.add_customer(john);
        myCustomerOrganizer.add_customer(meier);
        myCustomerOrganizer.add_customer(wurst);

        job transfer1 = new job(meier, wurst, 500.50);
        job transfer2 = new job(mueller, john, 77.00);

        myJobOrganizer.add_job(transfer1);
        myJobOrganizer.add_job(transfer2);

        System.out.println(myJobOrganizer.jobNumber);
        System.out.println(myJobOrganizer.all_jobs().toString());
    }
}

Answer 1

public int jobNumber = jobList.size();不会被更新，所以要这样做，这将返回当前的jobList，而不像您的字段那样存储它的实例。

public int jobNumber(){
  return jobList.size();
}

Answer 2

这是因为下面的代码是在对象创建时执行的，但此后不会执行，因此以后不会更新值。

public int jobNumber = jobList.size();

Java：为什么带有元素的ArrayList的打印输出为零？

2 个答案: