Java-如何更改“本地"?事件监听器中的变量 [英] Java - How to change a 'local?' variable within an event listener
问题描述
我想回答一个简短的问题,希望有人能回答.基本上,我有一个String变量,需要根据组合框的值进行更改,该组合框具有附加的事件侦听器.但是,如果我将字符串定为final,则无法更改,但是如果我不将其定为final,则日食mo吟表示该字符串不是final.最好(最简单)的解决方法是什么?
Got a quick question which I hope someone can answer. Basically I have a String variable which needs changing based upon the value in a combo box which has an event listener attached to it. However if I make the string final then it cant be changed, but if i don't make it final then eclipse moans that it isn't final. Whats the best (and simplest) work around?
代码如下
final String dialogOutCome = "";
//create a listener for the combo box
Listener selection = new Listener() {
public void handleEvent(Event event) {
//get the value from the combo box
String comboVal = combo.getText();
switch (comboVal) {
case "A": dialogOutCome = "a";
case "B": dialogOutCome = "b";
case "C": dialogOutCome = "c";
case "D": dialogOutCome = "d";
}
}
};
推荐答案
您不能.
考虑一下:
- 只要运行中声明的方法存在,本地变量就存在.
- 该方法调用结束后(通常是因为该方法存在),变量将消失
- 收听者可以(并且通常确实)寿命更长
那么当方法已经返回并且侦听器尝试修改局部变量时应该怎么办?
So what should happen when the method returned already and the listener tries to modify the local variable?
因为这个问题的答案不是一个很好的答案,所以他们决定通过不允许访问非 final
局部变量来使这种情况变为不可能.
Because this question does not have a really good answer, they decided to make that scenario impossible by not allowing access to non-final
local variables.
有两种方法可以解决此问题:
There are two ways around this problem:
- 尝试更改字段而不是局部变量(这也可能更适合于侦听器的生命周期)或
- 使用
final
局部变量,您可以更改其中的 content (例如,List
或String []
(带有单个元素).
- try to change a field instead of a local variable (this probably also fits better with the life-time of the listener) or
- use a
final
local variable, of which you can change the content (for example aList
or aString[]
with a single element).
这篇关于Java-如何更改“本地"?事件监听器中的变量的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!