带有整数的if语句 [英] if statement with integers

问题描述

我是Java新手.我正在寻找家庭作业方面的帮助.我最初不会发布完整的代码，但我认为它不会帮助我学习.

I'm new at Java. I'm looking for some help with homework. I wont post the full code I was doing that originally but I dont think it will help me learn it.

我有一个使用类的程序.我有一个可以验证选择内容的类，一个有我的设置者和getter者的类，以及一个由教授用该程序的IO编码的类(这是一本addres书)

I have a program working with classes. I have a class that will validate a selection and a class that has my setters and getters and a class that the professor coded with the IO for the program (it's an addres book)

我的主句中有这样的声明

I have a statement in my main like this that says

//create new scanner
Scanner ip = new Scanner(System.in);

System.out.println();
int menuNumber = Validator.getInt(ip, "Enter menu number: ", 1, 3);

if (menuNumber = 1)
{
    //print address book    
}

else if (menuNumber = 2)
{
    // get input from user
}
else 
{
    Exit
}

如果查看我的if语句 if(menuNumber = 1)，我会看到一条红线，告诉我不能将int转换为boolean.我以为答案是 if(menuNumber.equals(1))，但这也给了我类似的错误.

If you look at my if statement if (menuNumber = 1) I get a red line that tells me I cannot convert an int to boolean. I thought the answer was if (menuNumber.equals(1)) but that also gave me a similar error.

我不是100％可以解决该问题的方法，所以我想寻求帮助.我需要将条目转换为字符串吗?现在，我的验证器看起来像:

I'm not 100% on what I can do to fix it so I wanted to ask for help. Do I need to convert my entry to a string? Right now my validator looks something like:

if (int < 1)
print "Error entry must be 1, 2 or 3)
else if (int > 3) 
print "error entry must 1, 2, or 3)
else 
print "invalid entry"

如果我将main转换为字符串而不是int，是否还必须全部更改呢?

If I convert my main to a string instead of an int wont I have to change this all up as well?

再次感谢您，我还没有那么出色，我想把大部分的工作都淘汰掉.

Thanks again for helping me I haven't been diong that great and I want to get a good chunk of the assignment knocked out.

推荐答案

if (menuNumber = 1)

应该是

if (menuNumber == 1)

前者将值1分配给 menuNumber ，后者测试 menuNumber 是否等于1.

The former assigns the value 1 to menuNumber, the latter tests if menuNumber is equal to 1.

得到不能将int转换为boolean 的原因是Java期望 if(...)构造中的布尔值-但 menuNumber 是 int .表达式 menuNumber == 1 返回一个布尔值，这是必需的.

The reason you get cannot convert an int to boolean is that Java expects a boolean in the if(...) construct - but menuNumber is an int. The expression menuNumber == 1 returns a boolean, which is what is needed.

这是各种语言的常见混淆.我认为您可以设置Java编译器来警告您其他可能发生此错误的情况.

It's a common mix-up in various languages. I think you can set the Java compiler to warn you of other likely cases of this error.

某些语言中使用的一个技巧是反过来进行比较:(1 == menuNumber)，这样，如果您不小心键入 = ，您将获得一个编译器错误，而不是静默错误.

A trick used in some languages is to do the comparison the other way round: (1 == menuNumber) so that if you accidentally type = you will get a compiler error rather than a silent bug.

这被称为 Yoda条件.

在Java中，如果使用 .equals()方法(不是 == )比较对象，则可以使用类似的技巧，其中之一可能是空:

In Java, a similar trick can be used if you are comparing objects using the .equals() method (not ==), and one of them could be null:

if(myString.equals("abc"))

如果 myString 为null，则

可能会产生 NullPointerException .但是:

may produce a NullPointerException if myString is null. But:

if("abc".equals(myString))

可以应付，并且如果 myString 为null，则只会返回 false .

will cope, and will just return false if myString is null.

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