Java 无法从静态上下文问题引用非静态变量

在这段代码中，我需要创建扩展类basicaccount的对象，但我得到错误消息“非静态变量不能从静态上下文引用”，我能做得更好吗

public class BankAccount {
  private double balance;

  public BankAccount() {
    balance = 0;
  }

  public BankAccount(double initialBalance) {
    balance = initialBalance;
  }
  public void deposit(double amount) {
    double newBalance = balance + amount;
    balance = newBalance;
  }
   public void withdraw(double amount) {
    double newBalance = balance - amount;
    balance = newBalance;
  }

  public double getBalance() {
    return balance;
  }
class BasicAccount extends BankAccount {
    public BasicAccount(Double d) {
      balance = d;
    }
}
  class Main {
    public static void main(String args[]) {
      BankAccount account = new BasicAccount(100.00);
      double balance = account.getBalance(); //expected 100.00;
      account.withdraw(80.00);
      balance = account.getBalance(); //expected 20.00;
      account.withdraw(50.00);
      balance = account.getBalance(); //expected 20.00 because the amount to withdraw is larger than the balance
    }
  }
}

---

您似乎已将您的

BasicAccount

类放在

BankAccount

类中，使其成为一个内部类。这意味着如果没有现有的

BankAccount

实例，就无法实例化

BasicAccount

你可能不想那样做。我建议您在理解效果之前，避免将类放在其他类中

将

BasicAccount

和

Main

类移动到

BankAccount

类定义之外。

如果没有封装的

BankAccount

对象，则无法实例化非静态嵌套类（

BasicAccount

和

Main

）。要实例化

BasicAccount

您需要在现有

BankAccount

对象上调用

newbasicaccount（…）

BankAccount account = new BankAccount().new BasicAccount(0);

然而，我认为您可能不希望这样-如果是这样的话，我认为您应该将

BasicAccount

和

Main

从内部

BankAccount

让Main成为你的公共课

从BankAccount类中删除公共帐户

将主类移到BankAccount类之外

确保

static main（String[]args）

在

main

public类中

下面是它应该是什么样子

class BankAccount {
    private double balance;

    public BankAccount() {
        balance = 0;
    }

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

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

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

    public double getBalance() {
        return balance;
    }

    class BasicAccount extends BankAccount {
        public BasicAccount(Double d) {
            balance = d;
        }
    }
}

public class Main {
    public static void main(String args[]) {
        BankAccount account = new BasicAccount(100.00);
        double balance = account.getBalance(); // expected 100.00;
        account.withdraw(80.00);
        balance = account.getBalance(); // expected 20.00;
        account.withdraw(50.00);
        balance = account.getBalance(); // expected 20.00 because the amount to withdraw is larger than the balance
    }
}

---

你能在有警告的地方标出行吗？你好像把你的

BasicAccount

类放在你的

BankAccount

类里面，使它成为一个内部类。这意味着如果没有现有的

BankAccount

实例，就无法实例化

BasicAccount

。你可能不想那样做。在你知道自己在做什么之前，避免把类放在其他类中。这能回答你的问题吗？