The relationship between Java classes

Java introduces the association , aggregation relationships , synthetic relationships and dependencies
Incidentally introduction is-a, is-like-a,has-a

Relations between classes

Generalization

Between classes and class inheritance relationship between the interfaces and interface inheritance relationship

​

Realization relationship

Class implements the interface for

connection relation

The connection between the class and class, a class can know another class properties and methods used in the java language member variables embodied

Me me = new Me(new Friend()) // build relationships

• For example, the relationship between me and my friends

  • I can find my friend's address

  public class Friend{
      public String addr;
  }
  class Me{
      Friend f;
      public Me(Friend f){
          this.f = f;
      }
      // test
      public static void main(String[] args){
          Friend f = new Friend();
          Me me = new Me(f);
          System.out.println(me.f.addr)//获取朋友的地址
      }
  }
  

Aggregation relationship

Aggregation relationship is a relationship is a strong relationship , and is an integral part of the relationship. For example: car and tires

Relationship and associated with a different class association relationship on an equal level, and the relationship between the polymerization type and the like at different levels on behalf of a whole, a part of the representative

Aggregation relationship is the relationship between parts and the whole

Overall not rely on section

Nor on the part of the whole

Overall not decide lifecycle parts (not part of the relationship between humans and limbs aggregation relationship)

• For example, the relationship between the classroom and students

  public class Student{
      
  }
  public class ClassRoom{
      List<Student> s;
  }
  

THE RELATIONSHIP

Synthesis of relationship is also associated with a relationship, stronger than the aggregation relationship

And synthetic polymeric relationship relations are similar, except that:

RELATIONSHIP BETWEEN whole and the part are closely linked , the overall life cycle decision part of the life cycle

• For example, the relationship between humans and the limbs

  public class human{
      List<四肢> s;
  }
  

Dependencies

Dependency is weak, a weak association than one relationship

In the javalanguage reflected in: call return values, parameters, local variables and static methods

• E.g

  public class Test{
      public void m1(){
          User user = new User();//依赖关系
      }
  }
  class user{
  }
  

is-a/is-like-a/has-a

is-a

• Dog is a Animal

• It is-a relationship is inherited

  public class Animal{
      
  }
  class Dog extends Animal{
      
  }
  

is-like-a

• A is like a I

• is-like-a relationship is to achieve

  public Interface I{
      void m1();
  }
  class A implements I {
      public void m1(){
          
      }
  }
  

has-a

• A has a B

• has-a relationship comprising

  public class B{
      
  }
  class A{// A has a B
      private B b;
  }