What is polymorphic method in java?

问题

I'm studying java language for SCJP test.

It is little bit hard to understand "polymorphic method".

Could you explain it for me? or give me some links?

回答1:

"Polymorphic" means "many shapes." In Java, you can have a superclass with subclasses that do different things, using the same name. The traditional example is superclass Shape, with subclasses Circle, Square, and Rectangle, and method area().

So, for example

// note code is abbreviated, this is just for explanation
class Shape {
    public int area();  // no implementation, this is abstract
}

class Circle {
    private int radius;
    public Circle(int r){ radius = r ; }
    public int area(){ return Math.PI*radius*radius ; }
}

class Square {
    private int wid;
    Public Square(int w){ wid=w; }
    public int area() { return wid*wid; }
}

Now consider an example

Shape s[] = new Shape[2];

s[0] = new Circle(10);
s[1] = new Square(10);

System.out.println("Area of s[0] "+s[0].area());
System.out.println("Area of s[1] "+s[1].area());

s[0].area() calls Circle.area(), s[1].area() calls Square.area() -- and thus we say that Shape and its subclasses exploit polymorphic calls to the method area.

回答2:

Charlie's answer explains in simple terms what polymorphism is.

Continuing from there, this would be a "polymorphic method":

public void Shape CreateShape() {
    return new Circle(10);
}

It's "polymorphic" in the sense that its signature says you 're getting a Shape, but what you are really getting is a subclass of Shape. Since you don't know exactly what you are getting (could be a Circle, a Square, etc), you have to handle it using the interface of the super class (i.e., polymorphism).

I should mention that (possibly because I only have slight experience with Java) "polymorphic method" is an unfamiliar term so it might be used to mean something else. This is just my interpretation.

回答3:

Polymorphism is a process of representing 'one form in many forms'.

It is not a programming concept but it is one of the principle.

Example 1 :

class A
{
 void print(double d)
 {
  System.out.println("Inside Double");
 }
 void print(float f)
 {
  System.out.println("Inside Float");
 }
}
class B
{
 public static void main(String [ ] args)
 {
  A obj1 = new A();
  obj1.print(10.0);
 }
}


Output :

//save as : B.java
//compile as :javac B.java
//run as : java B

Inside Double

______________________


Example 2 :

class A
{
 void print(double d)
 {
  System.out.println("Inside Double");
 }
 void print(float f)
 {
  System.out.println("Inside Float");
 }
}
class B
{
 public static void main(String [ ] args)
 {
  A obj1 = new A();
  obj1.print(10.0f);
 }
}


Output :

//save as : B.java
//compile as :javac B.java
//run as : java B

Inside Float

_______________________

Example 3 :

class A
{
 void print(double d)
 {
  System.out.println("Inside Double");
 }
 void print(float f)
 {
  System.out.println("Inside Float");
 }
}
class B
{
 public static void main(String [ ] args)
 {
  A obj1 = new A();
  obj1.print(10);
 }
}


Output :

//save as : B.java
//compile as :javac B.java
//run as : java B

Inside Float

To know more - http://algovalley.com/java/polymorphism.php

回答4:

A method is signature polymorphic if all of the following are true:

It is declared in the java.lang.invoke.MethodHandle class.

It has a single formal parameter of type Object[].

It has a return type of Object.

It has the ACC_VARARGS and ACC_NATIVE flags set.

In Java SE 8, the only signature polymorphic methods are the invoke and invokeExact methods of the class java.lang.invoke.MethodHandle.

JVM specification 2.9. Special Methods

回答5:

A polymorphic method is a method that can take many forms. By that that I mean, the method may at different times invoke different methods.

Let's say you got a class Animal and a class Dog extends Animal and a class Cat extends Animal, and they all override the method sleep()

Then..

animal.sleep();

..can call different methods depending on the dynamic type stored in the variable animal

来源：https://stackoverflow.com/questions/4605669/what-is-polymorphic-method-in-java

标签

java

polymorphism

terminology