Java 可选 - If Else 语句
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Java Optional - If Else Statements
提问by uraza
So after some reading I've seen that
所以经过一些阅读后，我看到了
if (optional.isPresent()) {
//do smth
}
is not the preferred way to use Optional (http://www.oracle.com/technetwork/articles/java/java8-optional-2175753.html). But if I have an if-statement like this:
不是使用 Optional 的首选方式（http://www.oracle.com/technetwork/articles/java/java8-optional-2175753.html）。但是如果我有这样的 if 语句：
if (optional.isPresent()) {
car = getCar(optional.get());
} else {
car = new Car();
car.setName(carName);
}
Is this the best way to do this or is there a more recommended way?
这是最好的方法还是有更推荐的方法？
采纳答案by TheKojuEffect
You can use Optionalas following.
您可以使用Optional如下。
Car car = optional.map(id -> getCar(id))
.orElseGet(() -> {
Car c = new Car();
c.setName(carName);
return c;
});
Writing with if-elsestatement is imperative style and it requires the variable carto be declared before if-elseblock.
用if-else语句编写是命令式的，它需要car在if-else块之前声明变量。
Using mapin Optionalis more functional style. And this approach doesn't need variable declaration beforehand and is recommended way of using Optional.
使用mapinOptional是更实用的风格。而且这种方法不需要事先声明变量，推荐使用Optional.
回答by khelwood
If you can incorporate the name into the Carconstructor, then you can write this:
如果您可以将名称合并到Car构造函数中，那么您可以这样写：
car = optional.map(id -> getCar(id))
.orElseGet(() -> new Car(carName));
If you must call the setter separately from your constructor, you would end up with something like this:
如果必须与构造函数分开调用 setter，则最终会得到如下结果：
car = optional.map(id -> getCar(id))
.orElseGet(() -> {
Car c = new Car();
c.setName(carName);
return c;
});
回答by wilmol
To take it further, if you have multiple if (optional.isPresent())or if (obj != null)
更进一步，如果您有多个if (optional.isPresent())或if (obj != null)
You can do this:
你可以这样做：
(getN returns Optional<Car>)
（getN 返回Optional<Car>）
return get1().map(Optional::of)
.orElseGet(() -> get2()).map(Optional::of)
.orElseGet(() -> get3()).map(Optional::of);
I.e. would be like this using ifstatements
即会像这样使用if语句
Optional<Car> car = get1();
if (car.isPresent()){
return car;
}
car = get2();
if (car.isPresent()){
return car;
}
car = get3();
if (car.isPresent()){
return car;
}
return Optional.empty();
