Question

class BankAccount {
    private String firstname;
    private String lastname;
    private int ssn;
    private int accountnumber = 0;
    private double accountbalance = 0.0;

    BankAccount() {
        firstname = "John Smith";
    }

    BankAccount(String firstname, String lastname, int ssn) {
        int accountnumber;
        double accountbalance;
    }

    public String getName() {
        return firstname;
    }

    public double getBalance() {
        return accountbalance;
    }

    public void setAccountNumber(int accountnumber) {
        return accountnumber;
    }

    public boolean equals(BankAccount ba) {
        return this.accountbalance == ba.accountbalance;
    }

    public void deposit(double amount) {
        return this.accountbalance = this.accountbalance + amount;
    }

    public int withdraw(double amount) {
        this.accountbalance = this.accountbalance - amount;
        if(accountbalance < 0) {
            this.accountbalance = this.accountbalance + amount;
            return -1;
        }
        else
           return 0;
    }

    public String toString() {
        return firstname+lastname+"/n"+"social secuirty "+"ssn"+"/n"+"account number is "+
        "accountnumber" +"/n" +"Balance:" +"accountbalance" +"/n";
    }
}

错误是：

BankAccount.java:34: error: incompatible types: unexpected return value
return accountnumber;
       ^
BankAccount.java:47: error: incompatible types: unexpected return value
return this.accountbalance=this.accountbalance+amount;
                          ^
2 errors

我做错了什么？

Answer 1

void方法无法return。并且具有返回类型的方法必须return方法签名中指定的类型。

错误1

例如，查看此方法

 public void setAccountNumber(int accountnumber) {
   return accountnumber;
   }

哟无法从void方法返回。

那应该是

  public void setAccountNumber(int accountnumber) {
           this.accountnumber =accountnumber;
       }

其他方法也是如此。

错误2

public void deposit(double amount) {
        return this.accountbalance = this.accountbalance + amount;
    }

返回语句在语法上是错误的。你无法返回，因为它是无效的。那应该是

  public void deposit(double amount) {
            this.accountbalance = this.accountbalance + amount;
        }

Answer 2

public void setAccountNumber(int accountnumber) {
 return accountnumber;
 }

此处您的返回类型为void，而您的返回int。

Answer 3

public void setAccountNumber(int accountnumber) {
    return accountnumber;
}

public void deposit(double amount) {
    return this.accountbalance=this.accountbalance+amount;
}

......你是否试图返回void - 返回功能???

这是正确的：

public int setAccountNumber(int accountnumber) {
//     ^^^
    return accountnumber;
}

public double deposit(double amount) {
//     ^^^^^^
    return this.accountbalance=this.accountbalance+amount;
}

Answer 4

Forst Error是meyhod的返回类型为void，方法返回int。

 public void setAccountNumber(int accountnumber) {
    return accountnumber;
 }

将其更改为：

 public int setAccountNumber(int accountnumber) {
    return accountnumber;
 }

，第二件事是这对于用于获取变量的方法来说不是一个好名字，将方法名称更改为：

 public int getAccountNumber(int accountnumber) { // why is this argument???
    return accountnumber;
 }

还有一件事，你的方法

public void deposit(double amount) {
     return this.accountbalance = this.accountbalance + amount;
}

有同样的错误。它应该是：

public double deposit(double amount) { //change void to double
    return this.accountbalance + amount; //as suggested by SURESH ATTA
}

Answer 5

到目前为止，每个答案都是正确的，并指出了问题。这是一个尚未提及的。

您的equals方法无法正确覆盖父级：

public boolean equals(BankAccount ba) {
    return this.accountbalance == ba.accountbalance;
}

equals上Object的签名为public boolean equals(Object other)，以便可以将任何对象相互比较。您已将其更改为仅允许与违反合同的其他BankAccounts进行比较。

请改为尝试：

public boolean equals(BankAccount ba) {
    if (ba instanceof BankAccount) {
        return this.accountbalance == ((BankAccount) ba).accountbalance;
    }
    else {
        return false;
    }
}

不兼容的返回类型错误java

5 个答案: