Question

我是（非常）业余Java程序员，遇到了一些麻烦。本质上，我有2个类：A和B，其中B扩展了A。

在A中，我定义了一个创建一些ZonedDateTime对象的方法。我知道如何在B中创建A的实例，以便可以在B中执行A的方法，但是问题出在稍后需要直接访问该方法的ZonedDateTime对象时。我的第一个猜测是像这样访问它们：

// Assuming the ZonedDateTime objects, e.g. dateTimeA, are within ClassA's "methodA()" method...
ClassA objectA = new ClassA();
System.out.println(objectA.methodA().dateTimeA);

当这不可避免地出错时，我想我需要返回的方法，但是据我所知，这是不可能的。您只能返回某些数据类型，而不能返回对象。我还应该提到，我需要将这些对象保留为对象，因此将它们转换为String然后以这种方式返回它们对我来说是行不通的。

这个问题感觉很基础，但是即使如此，我也找不到其他答案。很抱歉，如果这是一个重复的问题。任何帮助将不胜感激。

修改（S）：

这里有更多代码可以使问题更容易重现：

WatchFaceEDIT（即A）：

import java.time.ZonedDateTime;
import java.time.ZoneId;
    
public class WatchFaceEDIT {
    
    // Up here are some variable declarations and things used in the switch statement below.
    
    public void watchFaceMethod(String userInput) { // userInput is a parameter passed up from a subclass of this class.
        
        switch (userInput) {
            case "1":
            ZonedDateTime dateTimeHere = ZonedDateTime.now();
            hour = dateTimeHere.getHour();
            minute = dateTimeHere.getMinute();
            amPM = dateTimeHere.getHour();
            break;
            
            case "2":
            ZonedDateTime dateTimeThere = ZonedDateTime.now(ZoneId.of("Europe/Paris"));
            hour = dateTimeThere.getHour();
            minute = dateTimeThere.getMinute();
            amPM = dateTimeThere.getHour();
            break;
            
            case "3":
            hour = -1;
            minute = -1;
            break;
        }
        // The rest of the code in WatchFaceEDIT does some things with these hour and minute variables.
    }
}

WatchEDIT（即B）：

import java.time.format.DateTimeFormatter;

public class WatchEDIT extends WatchFaceEDIT {
    
    static void watchMethod(String userInput) {

        WatchFaceEDIT watchFaceObject = new WatchFaceEDIT();
        watchFaceObject.watchFaceMethod(userInput);

        DateTimeFormatter dateTimeFormat = DateTimeFormatter.ofPattern("hh:mm a 'on' EEEE, MMMM dd, yyyy");
        String dateTimeDisplay = watchFaceObject.watchFaceMethod(userInput).dateTimeHere.format(dateTimeFormat);
        // There is more to the code than this, but the problem seems to be here.
    }
}

在这里我将简短地提到，我认为问题可能与switch语句的范围有关，但是在WatchEDIT中，我能够毫无问题地运行watchFaceMethod，并且该方法确实利用了创建的对象来显示事物。 / p>

Answer 1

我检查了您的初始post，以了解更多相关信息，并建议采用更合适的重构方式：

您不应在WatchEDIT中为static使用watchMethod －这样您就可以引用其超类的成员
移动WatchFaceEDIT中的打印功能以分隔方法
在WatchFaceEDIT::watchFaceMethod中设置所有相关值

话虽如此，代码修复如下：

public class WatchFaceEDIT {
    // instance variables set inside watchFaceMethod
    protected int hour;
    protected int minute;
    protected int amPM;
    protected ZonedDateTime dateTimeObject;

    public void watchFaceMethod(String userInput) {
        
        switch (userInput) {
            case "1":
                dateTimeObject = ZonedDateTime.now();
                hour = dateTimeHere.getHour();
                minute = dateTimeHere.getMinute();
                amPM = dateTimeHere.getHour();
                break;
                
            case "2":
                dateTimeObject = ZonedDateTime.now(ZoneId.of("Europe/Paris"));
                hour = dateTimeThere.getHour();
                minute = dateTimeThere.getMinute();
                amPM = dateTimeThere.getHour();
                break;
                
            case "3":
                dateTimeObject = null;
                hour = -1;
                minute = -1;
                amPM = -1;
                break;
        }
        printSomething();
    }
    
    public void printSomething() {
        // move here the printing code from watchFaceMethod
        // if needed you may override this method in WatchEDIT class to modify display
        // The rest of the code in WatchFaceEDIT does some things with these hour and minute variables.
    }
}

public class WatchEDIT extends WatchFaceEDIT {
    
    public void watchMethod(String userInput) {
        // call method defined in super class and set instance variables
        watchFaceMethod(userInput);
        
        DateTimeFormatter dateTimeFormat = DateTimeFormatter.ofPattern("hh:mm a 'on' EEEE, MMMM dd, yyyy");
        
        String dateTimeDisplay = dateTimeObject == null ? "N/A" : dateTimeObject.format(dateTimeFormat);
        
        // There is more to the code than this, but the problem seems to be here.
    }
}

仅创建子类实例的主类

// does not need to extend WatchEDIT/WatchFaceEDIT classes
public class Main {
    public static void main(String[] args) {
        
        WatchEDIT watchObject = new WatchEDIT();

        System.out.println("Welcome to Interactive Watch!\n");
        System.out.println("What would you like to do?");
        System.out.println("[1] See local time.");
        System.out.println("[2] See local time in a particular place.");
        System.out.println("[3] See something special.\n");
        
        Scanner scannerObject = new Scanner(System.in);
        
        boolean loopBreak = true;
        
        while (loopBreak) {
            
            loopBreak = false; // loopBreak set to false
            
            String userInput = scannerObject.nextLine(); // User inputs some string
            
            switch(userInput) {
                case "1":
                case "2":
                case "3":
                    watchObject.watchMethod(userInput);
                    break;
                
                default:
                    loopBreak = true; // loopBreak set to true; while loop reinitiates
                    System.out.println("\nPlease enter a valid key.\n");
                    break;
            }
        }
    }
}

如何在另一个对象的方法中访问一个对象？

1 个答案: