Static Binding and Dynamic Binding about 2122-s2

[yongchein-o]

Static Binding

Static binding means the compiler chooses the method based on the compile-time type.

class A {
  static void print() {
    System.out.println("This is superclass.");
  }
  static void print(String s) {
    System.out.println("This is superclass." + s);
  }
}

class B extends A {
  static void print() {
    System.out.print("This is subclass.");
  }
  static void print(int x) {
    System.out.println("This is subclass." + x);
  }
}

Let's say you run the above in jshell, this is the output:

jshell> A b = new B();
b ==> B@7cd62f43

jshell> b.print()
This is superclass.

jshell> b.print(1);
|  Error:
|  incompatible types: int cannot be converted to java.lang.String
|  b.print(1);
|          ^

jshell> b.print("Hello")
This is superclass.Hello

jshell> B b = new B()
b ==> B@53b32d7

jshell> b.print()
This is subclass.

jshell> b.print(1)
This is subclass.1

jshell> b.print("Hello");
This is superclass.Hello

As you can see when we have the variable b of type A, b.print() invokes the method in the superclass cos b is determined by the compiler at compile time to be of type A. It will "start" looking for the method in superclass A. I guess this is static binding.

Dynamic binding

Dynamic is just the compiler choosing which method to invoke based on the run time type of the target. I guess it will start looking for a matching method signature in the subclass first then work its way up.

I removed the static modifier:

jshell> b.print()
This is subclass.

Sorry for the various update. I think I was quite confused too. Maybe this might not be the best example. Hopefully prof can clarify.