JAVA：如何打印我的 CreditCard 对象的内容，而不是地址？ （我正在打印参考地址）[重复]

Question

我正在我的数据结构书中做一个练习，似乎我打印的是参考地址而不是实际内容？有人可以看看我的代码并帮助我吗？感谢您的宝贵时间。

public class CreditCard {
//  instance variables
private String customer;
private String bank;
private String account;
private int limit;
protected double balance;

// constructors - account for all cases, one with a bal, and one without
public CreditCard(String cust, String bk, String acnt, int lim, double bal){
    customer = cust;
    bank = bk;
    account = acnt;
    limit = lim;
    balance = bal;
}
public CreditCard(String cust, String bk, String acnt, int lim){
    this(cust, bk, acnt, lim, - 0.0);
}
// accessors
public String getCustomer(){return customer;}
public String getBank(){return bank;}
public String getAccount(){return account;}
public double getLimit(){return limit;}
public double getBalance(){return  balance;}

// updaters
public boolean charge(double price){
    if(price + balance > limit){
        return false;
    }
    else balance += price;
    return true;
}
public void makePayment(double amount){
    balance -= amount;
}

// utility (static)
public static void printSummary(CreditCard card){
    System.out.println("Customer = " + card.customer);
    System.out.println("Bank = " + card.bank);
    System.out.println("Account = " + card.account);
    System.out.println("Limit = " + card.limit);
    System.out.println("Balance = " + card.balance);
}

}// 结束类 CreditCard

Answer 1

添加toString 方法（只需覆盖一个）。

public class CreditCard {
    //  instance variables
    private String customer;
    private String bank;
    private String account;
    private int limit;
    protected double balance;

    // constructors - account for all cases, one with a bal, and one without
    public CreditCard(String cust, String bk, String acnt, int lim, double bal) {
        customer = cust;
        bank = bk;
        account = acnt;
        limit = lim;
        balance = bal;
    }

    public CreditCard(String cust, String bk, String acnt, int lim) {
        this(cust, bk, acnt, lim, -0.0);
    }

    // accessors
    public String getCustomer() {
        return customer;
    }

    public String getBank() {
        return bank;
    }

    public String getAccount() {
        return account;
    }

    public double getLimit() {
        return limit;
    }

    public double getBalance() {
        return balance;
    }

    // updaters
    public boolean charge(double price) {
        if (price + balance > limit) {
            return false;
        } else {
            balance += price;
        }
        return true;
    }

    public void makePayment(double amount) {
        balance -= amount;
    }

    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder("CreditCard{");
        sb.append("customer='").append(customer).append('\'');
        sb.append(", bank='").append(bank).append('\'');
        sb.append(", account='").append(account).append('\'');
        sb.append(", limit=").append(limit);
        sb.append(", balance=").append(balance);
        sb.append('}');
        return sb.toString();
    }

    // you do not need this util method because of it converts to
    public static void printSummary(CreditCard card) {
        System.out.println("CreditCard = " + card);
    }
}// end class CreditCard

Answer 2

你得到的是Object 类的toString() 实现。 引用自它的 javadoc：

结果应该是一个简洁但信息丰富的表示，易于人们阅读。建议所有子类重写此方法。

这意味着，您需要在 CreditCard 类中使用您自己的 toString() 实现来覆盖它。 可以这么简单：

@Override
public String toString() {
    return getClass().getName()
         + "[ customer = " + customer
         + ", bank = " + bank
         + ", account = " + account
         + ", limit = " + limit
         + ", balance = " + balance
         + "]";
}

如果你喜欢多行输出，你可以在上面的部分字符串中插入一些\n。

顺便说一句： 您不再需要您的方法public static void printSummary(CreditCard card)。 而不是使用

CreditCard.printSummary(creditCard);

你现在可以简单地使用

System.out.println(creditCard);

在后台调用您的 toString() 方法。