java 如何从另一个类更新一个类中的变量
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How to update a variable in one class from another class
提问by the_prole
I realize this is probably a really basic question, but I can't figure it out.
我意识到这可能是一个非常基本的问题，但我无法弄清楚。
Say I have this main class
说我有这个主课
public class Main{
public static void main(String[] args){
int a = 0;
AddSomething.addOne(a);
System.out.println("Value of a is: "+String.valueOf(a));
}
}
Here is AddSomethingclass and addOne()method
这是AddSomething类和addOne()方法
public class AddSomething{
public static void addOne(int a){
a++;
}
}
The addOnemethod is not adding anything
该addOne方法没有添加任何东西
System.out.println("Value of a is: "+String.valueOf(a));
// Prints 0 not 1
How can I make Addclass update variable ain Mainclass?
如何在课堂上制作Add类更新变量？aMain
采纳答案by Eran
addOnereceives a copy of a, so it can't change the avariable of your main method.
addOne接收 的副本a，因此它无法更改a您的 main 方法的变量。
The only way to change that variable is to return a value from the method and assign it back to a:
更改该变量的唯一方法是从该方法返回一个值并将其分配回a：
a = Add.addOne(a);
...
public int addOne(int a){
return ++a;
}
回答by midikko
Thats becouse primitive types in java pass to methods by value. Only one way to do what you want is reassign variable, like :
那是因为 java 中的原始类型按值传递给方法。只有一种方法可以做你想做的事是重新分配变量，比如：
public class Main{
public static void main(String[] args){
int a = 0;
a = Add.addOne(a);
System.out.println("Value of a is: "+String.valueOf(a));
}
}
and
和
public class AddSomething{
public static int addOne(int a){
return a++;
}
}
回答by Akoder
I know, Eran's answer is what you all need. But just to show another way, posting this answer.
我知道，Eran 的回答正是你们所需要的。但只是为了展示另一种方式，发布这个答案。
public class Main
{
static int a = 0;
public static void main(String[] args)
{
AddSomething.addOne();
System.out.println("Value of a is: "+a);
}
}
And in AddSomethingclass..
而在AddSomething课堂上..
public class AddSomething
{
public static void addOne(){ Main.a++ };
}
AddSomethingmust be in same package as Mainclass, as int ahas default access modifier.
AddSomething必须与Main类在同一个包中，因为int a具有默认访问修饰符。
