What are the uses of java design patterns?

Java design patterns are generally divided into three categories: creational patterns, structural patterns, and behavioral patterns. A design pattern will be introduced below.

The design pattern follows 6 principles:

1. Open Close Principle

Open for extension, closed for modification.

2. Liskov Substitution Principle

Only when the derived class can replace the base class and the function of the software unit is not affected, the base class can be truly reused. , and derived classes can also add new behaviors based on base classes.

3. Dependence Inversion Principle

This is the basis of the opening and closing principle. Interface programming relies on abstraction rather than concreteness.

4. Interface Segregation Principle

Use multiple isolation excuses to reduce coupling.

5. Demeter Principle (Demeter Principle)

An entity should interact with other entities as little as possible to make the system functional modules relatively independent.

6. Composite Reuse Principle

The principle is to use synthesis/aggregation as much as possible instead of inheritance. Inheritance actually destroys the encapsulation of the class, and the methods of the super class may be modified by the subclass.

Factory Method of Creational Pattern

The commonly used factory pattern is the static factory, which uses the static method as a similar For auxiliary effects such as common tool classes Utils, factory classes generally do not need to be instantiated.

interface food{}

class A implements food{}
class B implements food{}
class C implements food{}
public class StaticFactory {
    private StaticFactory(){}
    
    public static food getA(){  return new A(); }
    public static food getB(){  return new B(); }
    public static food getC(){  return new C(); }
}

class Client{
    //客户端代码只需要将相应的参数传入即可得到对象
    //用户不需要了解工厂类内部的逻辑。
    public void get(String name){
        food x = null ;
        if ( name.equals("A")) {
            x = StaticFactory.getA();
        }else if ( name.equals("B")){
            x = StaticFactory.getB();
        }else {
            x = StaticFactory.getC();
        }
    }
}

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