1. Simple factory model
- Example: Let us write a method of addition, subtraction, multiplication, and division. The initial wording is: (For the convenience of the denominator when the division is not determined
0)
public class Operation {
public static double getReault(double left ,double right,String op) {
double result = 0;
switch (op) {
case "+":
result = left+right;
break;
case "-":
result = left-right;
break;
case "*":
result = left*right;
break;
case "/":
result = left/right;
break;
default:
break;
}
return result;
}
}
Although this method extracts functions to a certain extent, it is not very beneficial for increasing calculations.
- When we use inheritance features, for example:
//首先定义一个父类
public class Operation {
private double left;
private double right;
public double getLeft() {
return left;
}
public void setLeft(double left) {
this.left = left;
}
public double getRight() {
return right;
}
public void setRight(double right) {
this.right = right;
}
public double getReault() {
return 0;
}
}
//第二步，创建加减乘除四个类继承Operation
public class OperationAdd extends Operation {
@Override
public double getReault() {
return this.getLeft() + this.getRight();
}
}
public class OperationSub extends Operation {
@Override
public double getReault() {
return this.getLeft() - this.getRight();
}
}
public class OperationMul extends Operation {
@Override
public double getReault() {
return this.getLeft() * this.getRight();
}
}
public class OperationDiv extends Operation {
@Override
public double getReault() {
return this.getLeft() / this.getRight();
}
}
//定义工厂类
public class OperationFactory {
public static Operation craeteOperation(String op) {
Operation operation = null;
switch (op) {
case "+":
operation = new OperationAdd();
break;
case "-":
operation = new OperationSub();
break;
case "*":
operation = new OperationMul();
break;
case "/":
operation = new OperationDiv();
break;
default:
break;
}
return operation;
}
}
//主函数测试类
public class Test {
public static void main(String[] args) {
Operation operation = OperationFactory.craeteOperation("+");
operation.setLeft(1);
operation.setRight(2);
System.out.println(operation.getReault());
}
}
At this time, we can dynamically create objects through the factory according to the input symbols to complete the addition, subtraction, multiplication, and division operations;
If there are new requirements, such as adding sqrtfunctions, you only need to create a class inheritance Operation. At first glance, the amount of code seems to increase, but the scalability of the code increases.
- Since the simple factory pattern can be implemented through inherited classes, so can interfaces. In this case, the interface may not have less code than the inherited class.
//首先定义一个接口
public interface Operation {
//将公共方法抽出定义在接口中
double getResult(double left,double right);
}
//加
public class OperationAdd implements Operation {
@Override
public double getResult(double left, double right) {
return left + right;
}
}
//减
public class OperationSub implements Operation {
@Override
public double getResult(double left, double right) {
return left - right;
}
}
//乘
public class OperationMul implements Operation {
@Override
public double getResult(double left, double right) {
return left * right;
}
}
//除
public class OperationDiv implements Operation {
@Override
public double getResult(double left, double right) {
return left / right;
}
}
//定义的工厂类没有什么变化
public class OperationFactory {
public static Operation craeteOperation(String op) {
Operation operation = null;
switch (op) {
case "+":
operation = new OperationAdd();
break;
case "-":
operation = new OperationSub();
break;
case "*":
operation = new OperationMul();
break;
case "/":
operation = new OperationDiv();
break;
default:
break;
}
return operation;
}
}
//主函数测试类
public class Test {
public static void main(String[] args) {
Operation operation = OperationFactory.craeteOperation("+");
System.out.println(operation.getResult(1, 3));
}
}
Reference material: Big talk design pattern, by Cheng Jie