设计模式之解释器模式22

设计模式之解释器模式22

背景

类图

代码实现

public abstract class Expression {

//解析公式与数值，其中var中的key值是公式中的参数，value值是具体的数字
public abstract int interpreter(HashMap<String,Integer> var);
}

public class VarExpression extends Expression{

private String key;

public VarExpression(String _key) {
this.key = _key;
}

@Override
public int interpreter(HashMap<String, Integer> var) {
return var.get(this.key);
}

}

public abstract class SymbolExpression extends Expression{

protected Expression left;

protected Expression right;

public SymbolExpression(Expression _left, Expression _right) {
this.left = _left;
this.right = _right;
}

}

public class AddExpression extends SymbolExpression{

public AddExpression(Expression _left, Expression _right) {
super(_left, _right);
}

@Override
public int interpreter(HashMap<String, Integer> var) {
return super.left.interpreter(var) + super.right.interpreter(var);
}

}

public class SubExpression extends SymbolExpression{

public SubExpression(Expression _left, Expression _right) {
super(_left, _right);
}

@Override
public int interpreter(HashMap<String, Integer> var) {
return super.left.interpreter(var) - super.right.interpreter(var);
}

}

public class Calculator {

private Expression expression;

public Calculator(String expStr) {

Stack<Expression> stacks = new Stack<Expression>();

char[] charArray = expStr.toCharArray();

Expression left = null;
Expression right = null;

for(int i=0; i<charArray.length; i++) {

switch (charArray[i]) {
case '+':
left = stacks.pop();
right = new VarExpression(String.valueOf(charArray[++i]));
stacks.push(new AddExpression(left, right));
break;
case '-':
left = stacks.pop();
right = new VarExpression(String.valueOf(charArray[++i]));
stacks.push(new SubExpression(left, right));
break;
default:
stacks.push(new VarExpression(String.valueOf(charArray[i])));
}
}
this.expression = stacks.pop();
}

public int run(HashMap<String,Integer> var) {
return this.expression.interpreter(var);
}

}

public class Client {

public static void main(String[] args) {
String expStr = "a+b-c";
HashMap<String,Integer> var = new HashMap<String, Integer>();
var.put("a", 100);
var.put("b", 5);
var.put("c", 10);

Calculator cal = new Calculator(expStr);
System.out.println(cal.run(var));
}
}

运行结果

95