A small template (an abstract class, a complete process is written in a method, the uncertain part is written in the abstract method, and then the subclass inherits the abstract class, and the subclas

  When testing ：main Function instantiates the object of the parent class , Instantiate objects of subclasses ,（ I have polymorphic subclass objects here ） Whatever can be executed is the method of the parent class , Then the template is completed

public class TemplateTest {
	public static void main(String[] args) {
		Template t = new SubTemplate();
		t.spendTime();
	}
}

abstract class Template {

	public void spendTime() {
		//  Calculate the time spent executing a piece of code 
		long start = System.currentTimeMillis();

		code();//  The uncertain part 、 The volatile part 

		long end = System.currentTimeMillis();

		System.out.println(" The time spent is :" + (end - start));
	}

	public abstract void code();//  Abstract methods , Subclass rewriting 
}

class SubTemplate extends Template {
	//  Subclass rewriting code Method 
	public void code() {
		//  Example ： Calculation 1000 The prime number within 
		for (int i = 2; i <= 1000; i++) {
			boolean isFlag = true;
			for (int j = 2; j < Math.sqrt(i); j++) {
				if (i % j == 0) {
					isFlag = false;
					break;
				}
			}
			if (isFlag) {
				System.out.println(i);
			}
		}
	}
}