解釋器模式-Interpreter 目前沒有想到其他更好的例子, 以後本文肯定重寫,或者儘力介紹得更到位....目前只是copy了iluwatar大神的代碼, 作為練習, 也方便自己以後查找本段代碼. Expression介面 表達式的統一定義. PlusExpression類 加法表達式. Min ...
解釋器模式-Interpreter
目前沒有想到其他更好的例子, 以後本文肯定重寫,或者儘力介紹得更到位....目前只是copy了iluwatar大神的代碼, 作為練習, 也方便自己以後查找本段代碼.
Expression介面
表達式的統一定義.
public interface Expression {
int interpret();
@Override
String toString();
}
PlusExpression類
加法表達式.
/**
* 加號
*/
public class PlusExpression implements Expression {
private Expression leftExpression;
private Expression rightExpression;
public PlusExpression(Expression leftExpression, Expression rightExpression) {
this.leftExpression = leftExpression;
this.rightExpression = rightExpression;
}
@Override
public int interpret() {
return leftExpression.interpret() + rightExpression.interpret();
}
@Override
public String toString() {
return "+";
}
}
MinusExpression類
減法表達式.
/**
* 減號
*/
public class MinusExpression implements Expression {
private Expression leftExpression;
private Expression rightExpression;
public MinusExpression(Expression leftExpression, Expression rightExpression) {
this.leftExpression = leftExpression;
this.rightExpression = rightExpression;
}
@Override
public int interpret() {
return leftExpression.interpret() - rightExpression.interpret();
}
@Override
public String toString() {
return "-";
}
}
MultiplyExpression類
乘法表達式.
/**
* 乘號
*/
public class MultiplyExpression implements Expression {
private Expression leftExpression;
private Expression rightExpression;
public MultiplyExpression(Expression leftExpression, Expression rightExpression) {
this.leftExpression = leftExpression;
this.rightExpression = rightExpression;
}
@Override
public int interpret() {
return leftExpression.interpret() * rightExpression.interpret();
}
@Override
public String toString() {
return "*";
}
}
NumberExpression類
數字也是一種表達式. 或者叫做語句中的一類元素
/**
* 數字
*/
public class NumberExpression implements Expression {
private int number;
public NumberExpression(int number) {
this.number = number;
}
public NumberExpression(String s) {
this.number = Integer.parseInt(s);
}
@Override
public int interpret() {
return number;
}
@Override
public String toString() {
return "number";
}
}
App類
運行/場景模擬
import java.util.Stack;
public class App {
public static void main(String[] args) {
String tokenString = "4 3 2 - 1 + *";
Stack<Expression> stack = new Stack<>();
String[] tokenList = tokenString.split(" ");
for (String s : tokenList) {
if (isOperator(s)) {
Expression rightExpression = stack.pop();
Expression leftExpression = stack.pop();
System.out.printf("popped from stack left: %s right: %s\n",
leftExpression.interpret(), rightExpression.interpret());
Expression operator = getOperatorInstance(s, leftExpression, rightExpression);
System.out.printf("operator: %s\n", operator);
int result = operator.interpret();
NumberExpression resultExpression = new NumberExpression(result);
stack.push(resultExpression);
System.out.printf("push result to stack: %s\n", resultExpression.interpret());
} else {
Expression i = new NumberExpression(s);
stack.push(i);
System.out.printf("push to stack: %s\n", i.interpret());
}
}
System.out.printf("result: %s\n", stack.pop().interpret());
}
private static boolean isOperator(String s) {
return s.equals("+") || s.equals("-") || s.equals("*");
}
private static Expression getOperatorInstance(String s, Expression left, Expression right) {
switch (s) {
case "+":
return new PlusExpression(left, right);
case "-":
return new MinusExpression(left, right);
case "*":
return new MultiplyExpression(left, right);
default:
return new MultiplyExpression(left, right);
}
}
}
運行結果如下:
