解释器模式
解释器模式解决某一领域重复出现的特定问题,使用普通编程方法极度复杂,需要这一特定领域的特定语法,解释器模式就是用来解释这种语法
类图:
比如解释加法和减法问题:
解释器:
public abstract class AbstractExpression {//此处也可以使用接口
public abstract Object interpreter();
}
public class Variable extends AbstractExpression {//变量
private int x;
public Variable(int x) {
this.x = x;
}
@Override
public Object interpreter() {
return x;
}
}
public class Add extends AbstractExpression {//加法
private AbstractExpression left;
private AbstractExpression right;
public Add(AbstractExpression left, AbstractExpression right) {
this.left = left;
this.right = right;
}
@Override
public Object interpreter() {
return (int) left.interpreter() + (int) right.interpreter();
}
}
public class Sub extends AbstractExpression {//减法
private AbstractExpression left;
private AbstractExpression right;
public Sub(AbstractExpression left, AbstractExpression right) {
this.left = left;
this.right = right;
}
@Override
public Object interpreter() {
return (int) left.interpreter() - (int) right.interpreter();
}
}
环境:
public class Context {
private String expression;
private AbstractExpression abstractExpression;
public Context(String expression) {
this.expression = expression;
String[] splits = expression.split(" ");
switch (splits[1]) {
case "+":
abstractExpression = new Add(new Variable(Integer.valueOf(splits[0])),
new Variable(Integer.valueOf(splits[2])));
break;
case "-":
abstractExpression = new Sub(new Variable(Integer.valueOf(splits[0])),
new Variable(Integer.valueOf(splits[2])));
break;
default:
break;
}
}
public String getResult() {
return expression + " " + abstractExpression.interpreter();
}
}
客户端:
public static void main(String[] args) {
Context ctx = new Context("10 + 30 =");
System.out.println(ctx.getResult());
Context ctx1 = new Context("10 - 30 =");
System.out.println(ctx1.getResult());
}
输出:
10 + 30 = 40
10 - 30 = -20
解释器模式使用范围不广,但是如果遇见某一特定问题,就显得很有用