Commonly used design patterns and anti-patterns in Java frameworks

Design patterns and anti-patterns in Java framework: Design patterns: Factory pattern: Simplifies object creation without specifying specific classes. Singleton mode: Ensure there is only one instance to facilitate the creation of global objects. Anti-Pattern: God Class: Too many behaviors and responsibilities, making the code difficult to maintain. Sausage anti-pattern: processes depend on each other, making code difficult to trace and execute.

Common design patterns and anti-patterns in Java frameworks

In Java frameworks, design patterns and anti-patterns are widely used to create flexible, maintainable code. This article will introduce some common design patterns and anti-patterns and demonstrate their application through practical cases.

Design Pattern

Factory Pattern:
Factory pattern is used to create instances of objects without specifying their concrete classes. It allows the creation of different types of objects without modifying client code.

public class Factory {

    public static Shape getShape(String type) {
        switch (type) {
            case "Circle":
                return new Circle();
            case "Rectangle":
                return new Rectangle();
            default:
                return null;
        }
    }
}

public class Main {

    public static void main(String[] args) {
        Shape shape = Factory.getShape("Circle");
        shape.draw();  // 输出：绘制圆形
    }
}

Singleton pattern:
The singleton pattern ensures that a class has only one instance. It is used to create global objects such as database connections.

public class Singleton {

    private static Singleton instance;

    private Singleton() {}

    public static Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

public class Main {

    public static void main(String[] args) {
        Singleton instance1 = Singleton.getInstance();
        Singleton instance2 = Singleton.getInstance();

        System.out.println(instance1 == instance2);  // 输出：true
    }
}

Anti-pattern

God class (God Object) anti-pattern:
The God class is a class that contains too many behaviors and responsibilities. This makes the code difficult to maintain and understand.

public class GodObject {

    // 大量的方法和字段...

    public void doSomething() {
        // 复杂的行为...
    }

    public void doSomethingElse() {
        // 另一个复杂的行为...
    }
}

Sausage Anti-Pattern (Spaghetti Code) Anti-Pattern:
The Spaghetti Code anti-pattern is a process with a large number of interdependencies in the code. This makes it difficult to understand and track code execution.

public class SpaghettiCode {

    public void foo() {
        bar();
        if (condition) {
            baz();
        } else {
            qux();
        }
    }

    public void bar() {
        // 依赖于 foo()
    }

    public void baz() {
        // 依赖于 foo()
    }

    public void qux() {
        // 依赖于 foo()
    }
}

By understanding and applying these design patterns and anti-patterns, developers can create more robust and maintainable Java framework code.

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