A. Eliminate coupling between the same types; b. Enable different objects to have multiple representations of the same behavior

For example, for the “dinosaur” class, the specific object can be “flying dragon” and “tyrannosaurus”, for the same “roar” behavior, the roar sound is different.

• Static type of a variable = reference type = compile-time variable: never changed, known to the compiler
• Dynamic type of variable = instance object type = runtime variable: changes, known at run time

See the following example:

Public class Test {// Human extends Human {} public class Test {// Human extends Human {} public class Test {// Human extends Human {} static Class Woman extends Human {} public static void main(String[] args) {Human = new man (); // Static type of variable man = reference type = compile-time variable = Human: will not change, in the compiler known // dynamic type of variable man = instance object type = runtime variable = man: will change, in the runtime known}}Copy the code

B = new B(); // compile time variable = A b, run time variable = new b () b.name; // call the parent class A member variable name b.move(); Move (), content() b.tent (); move () b.tent (); // Conclusion: Polymorphisms occur because the subclass object reference is assigned to the superclass object variable, i.e. A A = new B(), i.e. the compile-time variable is not the same as the run-time variableCopy the code

• To fully understand the implementation of polymorphism, the following is also necessaryJVMBasic knowledge of
• For:A a = new B()

A. Data storage mode

• Mainly includes: compile-time polymorphism & runtime polymorphism
• The implementations are: method overloading (Overload, pre-binding), method override (Override, post-binding)

In the next section, I will go into method Overload & method Override in detail.

• Defines the behavior of method dispatch based on the static type of a variable

  1. That is, determining which method to execute based on the static type of the variable
  2. It happens at compile time, so it doesn’tJavaVirtual machine to execute

• The principle of analytic

Public class Test {public class extends Human {} public class extends Human {} public class extends Human {} public class extends Human { Class Woman extends Human {} class Woman extends Human {} Public void sayHello(Human guy) {system.out.println (" Hello,guy!") ); } public void sayHello(Man guy) { System.out.println("hello gentleman!" ); } public void sayHello(Woman guy) { System.out.println("hello lady!" ); } public static void main(String[] args) {Human man = new man (); Man woman = new Woman(); Test test = new Test(); test.sayHello(man); test.sayHello(woman); }} // Run the result hello,guy! hello gentleman! A. Method OverLoad = static assignment = which method to execute based on the static type of the variable // b. SayHello (Human guy, man guy, man guy, man guy, man guy, man guy, man guy); SayHello (Human guy), sayHello(Man guy)Copy the code

• Defines the behavior of method dispatch based on the dynamic type of a variable

  That is, determining which method to execute based on the dynamic type of the variable

• The principle of analytic

Public void sayHello(){system.out.println ("Human say hello"); SayHello () class Man extends Human {@override protected void sayHello() {system.out.println (" Man ") say hello"); } } class Woman extends Human { @Override protected void sayHello() { System.out.println("woman say hello"); Public static void main(String[] args) {1 Human man = new man(); man.sayHello(); // situation 2 man = new Woman(); man.sayHello(); }} man say hello woman say hello Method Override = dynamic dispatch = Determine which method to execute (Override) based on the variable's dynamic type // 2. For case 1, the override sayHello() method in Man is called based on the variable's dynamic type (Man). For case 2: call overriding method sayHello() in woman based on variable (Man) dynamic type (woman)Copy the code

• In this article, we will focus on polymorphism, one of the three major features in Java. We will focus on its manifestation: method Overload, method Override.

• I’m going to continue to talk about Android & Java in more detail. If you’re interested, check out Carson_Ho’s Android development notes