Which methods are dynamically bound in Java?

Question

What the question says, which methods are dynamically bound in Java?

Coming from C++, if I am not mistaken, most methods are statically bound with a few exceptions.

Take a look at this article: http://geekexplains.blogspot.com/2008/06/dynamic-binding-vs-static-binding-in.html — Jon Lin, Sep 17 '11 at 08:17
Java non static methods are virtual by default. The jit optimises the code to minimise the overhead associated with doing this. Eg it can inline virtual methods. — Peter Lawrey, Sep 17 '11 at 09:44
http://download.oracle.com/javase/tutorial/javabeans/properties/bound.html http://download.oracle.com/javase/tutorial/uiswing/concurrency/bound.html — Samir Mangroliya, Sep 17 '11 at 08:26

Oak · Answer 1 · 2011-09-17T18:08:16.507

4

In theory, all methods are dynamically bound, with the exception of

Static methods
Constructors
Private methods
Final methods

In practice, at runtime the JVM may choose to JIT-compile some method calls to be statically resolved, for instance if there are no loaded classes containing an overriding method.

edited Sep 17 '11 at 18:08

answered Sep 17 '11 at 08:25

Oak

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Methods marked private and final in the parent class are statically bound too – NullUserException Sep 17 '11 at 14:43

jeha · Answer 2 · 2011-09-17T08:34:25.877

3

Instance method calls are resolved at runtime, static method calls are resolved at compile time.

edited Sep 17 '11 at 08:34

answered Sep 17 '11 at 08:20

jeha

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score 0 · Answer 3 · answered Sep 17 '11 at 09:15

In general you can think of it like thie: At compile time the compiler checks the static binding. At runtime the dinamic type is checked.

for Example:

Class A{
  public void function x(){ print("x"); }
}
Class B extends A{
  public void function x(){ print("y"); }
  public void function m(){ print("m"); }
}

public static void main(){
   A a = new B();
   a.x();        //1
   a.m();        //2
   ((B)a).m();   //3
}

in 1 will compile because the static type of a is A and A has a function called X, but at runtime there will be recognized a B object, and printed 'y'
in 2 there will be a compilation error because a is of type A and the class A has no function called m.
in 3 there will be checked if that inheritance B->A is legal, and then if class B has an function called m.

*notice that in the last case of casting, the compiler checks only the possibility of inheritance and not that there will be a B object. for example:

A a = new A();
((B)a).m();

will compile but throw a runntime exception.

Which methods are dynamically bound in Java?

3 Answers3