Java编译时和运行时多态的区别

多态这个词意味着有多种形式。简单来说，我们可以将多态性定义为消息以多种形式显示的能力。在本文中，我们将看到两种类型的多态性，编译时和运行时之间的区别。
编译时多态性：每当对象在编译时与其功能绑定时，这称为编译时多态性。在编译时， Java通过检查方法签名知道要调用哪个方法。所以这被称为编译时多态性或静态或早期绑定。编译时多态是通过方法重载实现的。方法重载表示在一个具有不同原型的类中可以有多个同名的函数。函数重载是实现多态的方法之一，但它取决于我们采用哪种类型的多态的技术。在Java，我们在编译时实现函数重载。下面是一个可以观察到编译时多态性的示例。

Java

// Java program to demonstrate
// compile-time polymorphism
public class GFG {
 
    // First addition function
    public static int add(int a, int b)
    {
        return a + b;
    }
 
    // Second addition function
    public static double add(
        double a, double b)
    {
        return a + b;
    }
 
    // Driver code
    public static void main(String args[])
    {
        // Here, the first addition
        // function is called
        System.out.println(add(2, 3));
 
        // Here, the second addition
        // function is called
        System.out.println(add(2.0, 3.0));
    }
}

输出：

5
5.0

运行时多态性：当对象在运行时与功能绑定时，这称为运行时多态性。运行时多态可以通过方法覆盖来实现。 Java虚拟机确定在运行时调用的正确方法，而不是在编译时。它也称为动态或后期绑定。方法覆盖表示子类具有与父类中声明的方法相同的方法。这意味着如果子类提供了由其父类之一提供的方法的特定实现，那么它被称为方法覆盖。以下是可以观察到运行时多态性的示例。

Java

// Java program to demonstrate
// runtime polymorphism
 
// Implementing a class
class Test {
 
    // Implementing a method
    public void method()
    {
        System.out.println("Method 1");
    }
}
 
// Defining a child class
public class GFG extends Test {
 
    // Overriding the parent method
    public void method()
    {
        System.out.println("Method 2");
    }
 
    // Driver code
    public static void main(String args[])
    {
        Test test = new GFG();
 
        test.method();
    }
}

输出：

Method 2

下表展示了运行时多态性和编译时多态性之间的区别：

Sr.No	Compile Time Polymorphism	Run time Polymorphism
1	In Compile time Polymorphism, the call is resolved by the compiler.	In Run time Polymorphism, the call is not resolved by the compiler.
2	It is also known as Static binding, Early binding and overloading as well.	It is also known as Dynamic binding, Late binding and overriding as well.
3	Method overloading is the compile-time polymorphism where more than one methods share the same name with different parameters or signature and different return type.	Method overriding is the runtime polymorphism having same method with same parameters or signature, but associated in different classes.
4	It is achieved by function overloading and operator overloading.	It is achieved by virtual functions and pointers.
5	It provides fast execution because the method that needs to be executed is known early at the compile time.	It provides slow execution as compare to early binding because the method that needs to be executed is known at the runtime.
6	Compile time polymorphism is less flexible as all things execute at compile time.	Run time polymorphism is more flexible as all things execute at run time.