从主外部的方法访问类对象

Question

Sorry if the title isn't as accurate as it should be or maybe even falesly translated on my part. I'm german and a beginner in coding so take it easy one me. So I coded a programm in JAVA. It is a programm for a bank account that I picked up in a book and tried to expand. Now, to keep it simple in this thread I obviously reduced my example code on the problem.

public class Test1 {
public static void method(){
    k.setNumber(300);  // This is where the problem is. From this method 
                       // I cannot acces the in main created class 
                       // object from 'Test'
    }

public static void main(String[] args) {

    Test k = new Test();

    method();
    k.getNumber();

}

}

Now the class 'Test:

public class Test {

int number;

public int getNumber(){
    return number;
}

public void setNumber(int nr){
    number = nr;
}
}

So is there any way around it? Otherwise I would have to write everything in the 'main', which is no problem in the case of this example, but in my original code thats not so easy to do.

Thanks for any help and advise. Hopefully this wasn't posted before because I already searched this site and the web.

Answer 1

Currently, k only belongs to the main method. To access it from other methods within the same class, you need to make it a class variable. This should be what you need:

public class Test1 {
    private static Test k;

    public static void method() {
        k.setNumber(300);
    }

    public static void main(String[] args) {
        k = new Test();
        method();
        k.getNumber();
    }
}

Answer 2

You can also use it as variable for your method :

public class Test1 {

public static void method(Test test){
    test.setNumber(300); 
}

public static void main(String[] args) {
  Test k = new Test();

  method(k);
  k.getNumber();
 }

}

Answer 3

you need to define

Test K = new Test()

outside of either methods, ie main and method. Mostly you need to make 'K' global to be visible to both methods.

Answer 4

you can do it as:

    public class Test1 {
public static void method(Test k){
    k.setNumber(300);  // This is where the problem is. From this method 
                       // I cannot acces the in main created class 
                       // object from 'Test'
    }

public static void main(String[] args) {

    Test k = new Test();

    method(k);//pass this test class instance to method
    k.getNumber();

}

}

Answer 5

You can either set k to be a global variable or you can pass it in the parameters of method like so.

public static void main( String[] argv )
{
    final Test k = new Test();

    method( k );
    System.out.println(  k.getNumber() );
}

public static void method(Test k)
{
    k.setNumber( 2 );
}