java 预期变量
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Variable expected
提问by Andrew Tobilko
private void calculateForEachQuestion() {
...
if (questions.size() >= answers.size()) {
answers.forEach(answer -> {
if (questions.contains(answer))
this.answer.setPoints((this.answer.getPoints())++);
// Variable expected ^
});
}
The error I encountered is:
我遇到的错误是：
unexpected type
required: variable
found: value
需要意外类型：
找到的变量：值
What is wrong with the statement?
声明有什么问题？
this.answer.setPoints((this.answer.getPoints())++);
回答by qwwqwwq
The ++operator only makes sense when applied to a declared variable.
在++当应用于声明的变量操作才有意义。
This operator will add one to an integer, long, etc. and save the result to the same variable in-place.
此运算符会将 1 添加到 an integer、long等，并将结果就地保存到相同的变量中。
If there is no declared variable, there is nowhere to save the result, which is why the compiler complains.
如果没有声明变量，则结果无处保存，这就是编译器抱怨的原因。
One way to allow use of the ++operator in this situation would be (not the most concise code, but to illustrate the point):
++在这种情况下允许使用运算符的一种方法是（不是最简洁的代码，而是为了说明这一点）：
int myVariable = this.answer.getPoints();
myVariable++;
this.answer.setPoints(myVariable);
回答by user3437460
this.answer.getPoints()will return a value, and you can't use increment ++or decrement --on that. You can only use it on variables.
this.answer.getPoints()将返回一个值，您不能对其使用增量++或减量--。您只能在变量上使用它。
If you want to add 1 to it, you can do it as:
如果你想给它加 1，你可以这样做：
this.answer.setPoints((this.answer.getPoints())+1);
I know that, but why?
我知道，但为什么呢？
You can do this:
你可以这样做：
int x = 5;
x++; // x is a variable and can have value 6
but not this:
但不是这个：
5++; // 5 is a value and can't have value 6
回答by Atri
Change this:
改变这个：
this.answer.setPoints((this.answer.getPoints())++);
to:
到：
this.answer.setPoints((this.answer.getPoints())+1);
++will increment a variable with 1, but since this.answer.getPoints()will return a value and its not a defined variable, it won't be able to store the incremented value.
++将用 1 增加一个变量，但由于this.answer.getPoints()将返回一个值而不是一个定义的变量，它将无法存储增加的值。
Think of it like doing:
this.answer.getPoints() = this.answer.getPoints() + 1, where would the incremented value be stored?
把它想象成：
this.answer.getPoints() = this.answer.getPoints() + 1，增加的值将存储在哪里？
回答by Paul Hicks
The error is just in this bit:
错误就在这一点上：
(this.answer.getPoints())++
The first part of this (this.answer.getPoints())creates an rvalue: effectively, an anonymous variable that lasts almost no time.
第一部分(this.answer.getPoints())创建了一个右值：实际上，一个几乎没有时间持续的匿名变量。
The second part ++increments that anonymous variable afterit is passed into setPoints().
第二部分++增量匿名变量后，它被传递到setPoints()。
Then, the anonymous variable (now incremented) is thrown away.
然后，匿名变量（现在递增）被丢弃。
The compiler/IDE knows that you're doing something that will never be used (incrementing a temporary value), and is flagging it.
编译器/IDE 知道您正在做一些永远不会被使用的事情（增加一个临时值），并且正在标记它。
