Formal parameters :

         Reference type

Interface : What you need is an implementation class object for the interface

It's nothing at this time , It's similar to the explanation of abstract classes .


interface Love {
public abstract void love();
} class LoveDemo {
public void method(Love l) {
l.love();// If you see that the reference type in a method is an interface type , What should be passed here is the implementation class object of the interface .
} // Define specific class implementation interface , The implementation class of this interface
class Teacher implements Love {
public void love() {
System.out.println(" Formal parameters are interface types ");
} class TeacherTest {
public static void main(String[] args) {
// demand : test LoveDemo Class love() Method
LoveDemo ld = new LoveDemo();
Love l = new Teacher();// It belongs to polymorphism
Teacher t = new Teacher();
return type
Reference type :
Interface : What is returned is the object of the implementation class of the interface
// Define a hobby interface
interface Love {
public abstract void love();
} class LoveDemo {
public Love getLove() { return new Teacher();// Anonymous object
} // Define specific class implementation interface
class Teacher implements Love {
public void love() {
System.out.println(" The return value type is the interface type ");
} class TeacherTest2 {
public static void main(String[] args) {
LoveDemo ld = new LoveDemo();
Love l = ld.getLove(); // It's polymorphic
l.love();// Can be called

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