java - 已在 null 中定义的类

Question

当我尝试继承时，出现错误“CheckingAccount 已在 null 中定义”。这是什么意思，我该如何解决？
这是我拥有的代码：

public class BankAccount 
{
    double balance;

    public void Bankaccount() {
        balance = 0;
    }

    public BankAccount(double initialBalance) {
        initialBalance = balance;
    }

    public void deposite(double amount) {
        balance = balance + amount;
    }

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

    public double getBalance(double balance) {
        return balance;
    }

    public void transfer(double amount, double bankAccountOther) {
        balance = balance - amount;

    }
}

public class CheckingAccount 
{
    public class CheckingAccount extends BankAccount {
    }
}

谁能帮帮我，我真的不明白这是什么意思

Answer 1

您在其内部定义了相同的类，这就是问题所在：

public class CheckingAccount {
    public class CheckingAccount extends BankAccount{
    }
}

内部类应该以不同的方式命名。或者，也许您打算扩展外部类BankAccount？目前尚不清楚您要实现什么，但也许这就是您的目标：

public class CheckingAccount extends BankAccount{
}

Answer 2

答案已经成功给出了很多次，但我会添加一个无关的评论，关于这段代码：

//constructor
    public void Bankaccount()
    {
    balance = 0;
    }

这不是构造函数。如果你想让它成为一个构造函数，你必须删除void

Answer 3

Your error is most likely right here:

public class CheckingAccount {
public class CheckingAccount extends BankAccount{

    }
}

You're defining a CheckingAccount class within an already existent CheckingAccount class. I don't think you can hide an enclosed type.

Answer 4

1   class CheckingAccount {
2   public class CheckingAccount extends BankAccount {
3
4        }
5   }

remove 1st and 5 line above and add no-argument constructor in Super class

Answer 5

你应该只写 -

public class CheckingAccount extends BankAccount{

    }

并不是

public class CheckingAccount {
    public class CheckingAccount extends BankAccount{

        }
    }

Answer 6

替换以下内容：

public class CheckingAccount {
public class CheckingAccount extends BankAccount{

    }
}

这样 ：

 public class CheckingAccount extends BankAccount{

 }

Answer 7

另一个并不是真正答案的旁注：

public BankAccount(double initialBalance) {
        initialBalance = balance;
    }

应该

public BankAccount(double initialBalance) {
        balance = initialBalance;
    }

因为前者一事无成。