主要对象的方法

Question

Is it possible to instantiate an object in a method within a class and then use one of the methods of the instantiated objects within main? Can I fix the following code?

    public class Test {

    public void Testmethod()  {

        someclass a = new someclass();

    }

    public static void main(String[] args) {

        a.methodfromsomeclass(); 

    }

}

Answer 1

There are three problems you need to fix:

1) You've declared a to be a local variable inside Testmethod . This means it can be accessed only inside Testmethod . If you want a variable that will live even after Testmethod is done executing, you should make it an instance variable of Test . That means that an instance of Test will contain the variable, and instance methods of Test , other than Testmethod will be able to access it.

Declaring an instance variable looks something like this:

public class Test {
    private someclass a;  // please choose a better variable name
    //...... other code ..........//
}

2) main won't be able to access the instance variable, because main is static. You can't make main non-static, either; Java requires it to be static. What you should do is write an instance method (called doMainStuff , for example, or some better name), and have your main create a new Test object, something like:

public void doMainStuff() {
     // something that calls Testmethod
     a.methodfromsomeclass(); // use a better name than "a"
     // other code
}

public static void main(String[] args) {
     new Test().doMainStuff();
}

3) The way you've written it so far, a new someclass would never be constructed, since you never call Testmethod . You'll need to make sure you call Testmethod before you try to use a . (It doesn't automatically get called just because it appears in the code. You have to write code that calls it.)

Also, please obey proper naming conventions: classes begin with an upper-case letter ( SomeClass ), methods begin with a lower-case letter ( testMethod ), and if a name has multiple words, the second and later words begin with upper-case letters.