重写和实现toString

Question

public class Student {

// Instance Variables
private String name;
private int age;
private String address;

// Default Constructor
public Student() {
    this("Not Given", 0, "Not Given");
}

// Parameterized constructor that takes in values
public Student(String name, int age, String address) {
    this.name = name;
    this.age = age;
    this.address = address;
}

// Getters and Setters
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}

public int getAge() {
    return age;
}
public void setAge(int age) {
    this.age = age;
}

public String getAddress(){
    return address;
}
public void setAddress(String address) {
    this.address = address;
}

// toString() to be overriden
@Override
public String toString() {
    return "Name: " + this.name + "\n" + "Age: " + this.age + "\n" + "Address: " + this.address;
}
}

`

public class MealCard {

private static int numberOfMealCards;
private final static int DEFAULT_BALANCE = 1000;
private int itemValue;
private int topUpValue;
public int newBalance;

// Getters and Setters
public int getItemValue() {
    return itemValue;
}
public void setItemValue(int itemValue) {
    this.itemValue = itemValue;
}

public int getTopUpValue() {
    return topUpValue;
}
public void setTopUpValue(int topUpValue) {
    this.topUpValue = topUpValue;
}

// purchaseItem method for when students buy food
public int purchaseItem() {
    newBalance = DEFAULT_BALANCE - itemValue;
    return newBalance;
}

// purchasePoints method for students topping up their meal card balance
public int purchasePoints() {
    newBalance = DEFAULT_BALANCE + topUpValue;
    return newBalance;
}

// Overriden toString method
@Override
public String toString() {
    return "Name: " + getName + "\n" + "Age: " + getAge + "\n" + "Address: " + getAddress +
            "\n" + "Meal Card Balance: " + newBalance + "\n" + "Number of Meal Cards: " + numberOfMealCards;
}

}

Answer 1

我认为用一个答案来说明这一点比用大量的评论来说明要容易得多。

在类中提供ToString的实现，归结起来就是提供该类的String表示，仅此而已。您要做的是为一个不相关的类(student)提供字符串信息，mealcard对这个类一无所知（也不应该）。

实现所需目标的方法可能是让student更新以保存对mealcard的引用（阅读：每个学生都有一个mealcard)，并且在toString的student实现中，使用您的饭卡引用从饭卡类获取toString数据。

public class MealCard {

    //... skipped over for simplicity

    @Override
    public String toString() {
        return "Item Value = " + this.getItemValue() + ", TopUpValue = " + this.getTopUpValue() + " ... "; // and so on...
    } 
}

public class Student {

    // other student data
    MealCard mealCard;  // set in constructor

    // ... other methods

    @Override
    public String toString() {
        return " ... other student data... MealCard = " + getMealCard().toString(); // use the mealcard reference to get string info

    }
}