不兼容的返回类型错误java

Incompatible return type error java

提问by higgs

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";
    }
}

Error is :

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

What am I doint wrong?

我做错了什么？

回答by Suresh Atta

A voidmethod cannot returnsometing. And a method which have a return type must returnthe type specified in method signature.

一个void方法不能returnsomething。并且具有返回类型的方法必须return是方法签名中指定的类型。

Error 1

错误 1

For example look this method

例如看这个方法

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

Yo cannot return from a voidmethod.

你不能从void方法返回。

That should be

那应该是

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

Same goes for remaining methods too.

其余方法也是如此。

Error 2

错误 2

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

that return statement is syntactically wrong. You cannot return as it is void. That should be

该 return 语句在语法上是错误的。您无法返回，因为它是无效的。那应该是

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

回答by Prashant Gurav

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

here your return type is voidand your returning int.

这里你的返回类型是void你的返回int。

回答by ikh

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

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

...Are you trying to return in void-return function???

...你是想在void-return 函数中返回吗？？？

This will be correct:

这将是正确的：

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

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

回答by Ankit Lamba

Forst Error is that the return type of your meyhod is voidand the method returns an int.

Forst 错误是您void的方法的返回类型是并且该方法返回一个int.

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

Change it to :

将其更改为：

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

and the second thing is this is not a good name for a method which is used for getting the variable, change the name of method to :

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，请将方法名称更改为：

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

One more thing,your method

还有一件事，你的方法

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

has the same error. It should be :

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
}

回答by Brandon

Every answer so far is correct and points out problems. Here is one that is not yet mentioned.

到目前为止，每个答案都是正确的，并指出了问题。这是尚未提及的一项。

Your equalsmethod does not properly over-ride the parent:

您的equals方法没有正确覆盖父级：

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

The signature of equalson Objectis public boolean equals(Object other)so that any objects can be compared to each other. You have changed it to only allow comparing against other BankAccounts, which violates the contract.

的签名equals上Object是public boolean equals(Object other)这样，任何对象可以相互比较。您已将其更改为仅允许与其他 BankAccounts 进行比较，这违反了合同。

Try this instead:

试试这个：

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