Java.util.Date 空输出

Question

我不知道为什么我的代码为 java.util.date 提供了 null。

问题:编写一个测试程序，创建一个Account对象，账户ID为1122，余额为20000，年利率为4.5%。使用提款方法提取 2500 美元，使用存款方法存入 3000 美元，并打印余额、月利息以及该帐户创建的日期
这是我的代码:

import java.util.*;  
public class Account {  
private int ID;  
private double Balance;  
private double annualInterestRate;  
private java.util.Date dateCreated;  
public Account(){}  
public Account(int ID, double Balance, double annualInterestRate){  
    this.ID=ID;  
    this.Balance=Balance;  
    this.annualInterestRate= annualInterestRate;  
}  
public void setID(int ID){  
    this.ID=ID;  
}
public void setBalance(double Balance){  
    this.Balance=Balance;  
}  
public void setAnnualInterestRate(double annualInterestRate){  
    this.annualInterestRate= annualInterestRate;  
}  
public int getID(){  
    return ID;  
}  
public double getBalance(){  
    return Balance;  
}  
public double getInterestRate(){  
    return annualInterestRate;  
}  
public java.util.Date getDateCreated(){  
    return dateCreated;  
}  
public double getMonthlyInterestRate(){  
    return annualInterestRate/12;  
}  
public void withDraw(double val){  
    if ((Balance - val) <0)  
    {  
        System.out.println("Offensive content removed from this line");  
    }  
    else  
    {  
        Balance -= val;  
    }  
}  
public void dePosits(double value){  
    Balance += value;  
}  

public static void main(String [] arges){  
Account account = new Account(1122, 20000,.045);  
account.withDraw(2500);  
account.dePosits(3000);  
System.out.println(account.getBalance());  
System.out.println(account.getDateCreated());  
}   

}

Answer 1

您尚未初始化dateCreated。例如，在构造函数中(或其他地方，具体取决于您的用例)

dateCreated = new java.util.Date();  

或使用所需日期进行初始化的任何其他方式。