In Java, Find the static object that called a method from inside the method

Question

I have classes similar to these:

class MyClass1 {

  static MyObject obj = new MyObject();

  public static void doSomething()
  { 
    MyClass1.obj.print();
    MyClass2.obj.print();
  } 

}    

class MyClass2 {

  static MyObject obj = new MyObject();

  public static void doSomething()
  {
    MyClass1.obj.print();
    MyClass2.obj.print();
  }

}

public class MyObject {

  public void print()
  {
    System.out.println("Which object called me?");
  }

}

From the print function in MyObject, how can I determine which object called the print function, the one in MyClass1, or the one in MyClass2?

Using a stack trace, I was only able to find the function that the print method is inside of and the class of the function that the print method is inside of.

Doing so, doesn't seem to be useful. Why do you need to determine the `print()` method is being invoked by which object? — Lion, Jul 21 '12 at 23:46
The MyObject class could contain important information about MyClass1 or MyClass2 and could contain a function that updates that information. Sometimes it is important to know whose information was just updated. — Scott Seto, Jul 21 '12 at 23:50

Arne · Answer 1 · 2012-07-22T00:03:46.683

just

public void print()
{
    System.out.println("Which object called me?");
    if (MyClass1.obj == this) {
        System.out.println("MyClass1");
    } else if (MyClass2.obj == this) {
        System.out.println("MyClass2");
    }
}

...as long as both obj fields are initialized.

but, hmm, I wouldn't do this. Better tell MyObject this upon construction, give print a parameter or sub-class MyObject in MyClass1 and MyClass2 and override print.

score 0 · Accepted Answer · answered Jul 22 '12 at 00:13

Why don't you make this is a first-class concept in your object model?

class MyClass1 {
    private static MyObject obj = new MyObject("MyClass1");
    public static void doSomething() {
        MyClass1.obj.print();
        MyClass2.obj.print();
    }
}

class MyClass2 {
    private static MyObject obj = new MyObject("MyClass2");
    public static void doSomething() {
        MyClass1.obj.print();
        MyClass2.obj.print();
    }
}

class MyObject {
    private final String name;
    MyObject(String name) {
        this.name = name;
    }

    public void print() {
        System.out.println("Q: Which object called me?");
        System.out.println("A: " + name);
    }
}

Instead of the String, you can also use the `Class` object (`MyClass1.class` or `MyClass2.class`) as the identifier. — Binil Thomas, Jul 22 '12 at 05:49

score -1 · Answer 3 · edited May 23 '17 at 11:56

-1

The following code should work:

public class MyObject {
    public static void main(String... args){
        MyClass2.doSomething();
    }


  public void print()
  {
    System.out.println(Thread.currentThread().getStackTrace()[2].getClassName() + " has me called.");
  }
}

See more at: http://download.oracle.com/javase/6/docs/api/java/lang/StackTraceElement.html or Get current stack trace in Java

edited May 23 '17 at 11:56

Community

1
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answered Jul 21 '12 at 23:57

Matt3o12

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this only prints the name of the class that contains the `doSomething` method - and that was already mentioned in the question. – Arne Jul 22 '12 at 00:02

In Java, Find the static object that called a method from inside the method

3 Answers3