模板方法模式Template Method

//Purpose. Template Method design pattern

//1. Standardize the skeleton of an algorithm in a base class "template" method
//2. Common implementations of individual steps are defined in the base class
//3. Steps requiring peculiar implementations are "placeholders" in base class
//4. Derived classes can override placeholder methods
//5. Derived classes can override implemented methods
//6. Derived classes can override and "call back to" base class methods

abstract class Generalization {
	// 1. Standardize the skeleton of an algorithm in a "template" method
	public void findSolution() {
		stepOne();
		stepTwo();
		stepThr();
		stepFor();
	}

	// 2. Common implementations of individual steps are defined in base class
	protected void stepOne() {
		System.out.println("Generalization.stepOne");
	}

	// 3. Steps requiring peculiar impls are "placeholders" in the base class
	abstract protected void stepTwo();

	abstract protected void stepThr();

	protected void stepFor() {
		System.out.println("Generalization.stepFor");
	}
}

abstract class Specialization extends Generalization {
	// 4. Derived classes can override placeholder methods
	// 1. Standardize the skeleton of an algorithm in a "template" method
	protected void stepThr() {
		step3_1();
		step3_2();
		step3_3();
	}

	// 2. Common implementations of individual steps are defined in base class
	protected void step3_1() {
		System.out.println("Specialization.step3_1");
	}

	// 3. Steps requiring peculiar impls are "placeholders" in the base class
	abstract protected void step3_2();

	protected void step3_3() {
		System.out.println("Specialization.step3_3");
	}
}

class Realization extends Specialization {
	// 4. Derived classes can override placeholder methods
	protected void stepTwo() {
		System.out.println("Realization   .stepTwo");
	}

	protected void step3_2() {
		System.out.println("Realization   .step3_2");
	}

	// 5. Derived classes can override implemented methods
	// 6. Derived classes can override and "call back to" base class methods
	protected void stepFor() {
		System.out.println("Realization   .stepFor");
		super.stepFor();
	}
}

public class TemplateMethodDemo {
	public static void main(String[] args) {
		Generalization algorithm = new Realization();
		algorithm.findSolution();
	}
}