设计模式之---解释器模式

解释器模式是个不怎么常用的设计模式。我们先来举一个简单的例子说明它。

a+b-c这么一个表达式，+,-都是非终结符表达式，a,b,c都是终结符表达式。非终结表达式一般是文法中的运算符或者关键字，而终结表达式一般是文法中的运算单元。

package interpreter;

import java.util.HashMap;
import java.util.Map;

public class Context {
private final Map<String, Integer> valueMap = new HashMap<String, Integer>();

public void addValue(final String key, final int value) {
valueMap.put(key, Integer.valueOf(value));
}

public int getValue(final String key) {
return valueMap.get(key).intValue();
}
}

package interpreter;

public abstract class AbstractExpression {
public abstract int interpreter(Context context);
}

package interpreter;

public class AddNonterminalExpression extends AbstractExpression {
private final AbstractExpression left;
private final AbstractExpression right;

public AddNonterminalExpression(final AbstractExpression left, final AbstractExpression right) {
this.left = left;
this.right = right;
}

@Override
public int interpreter(final Context context) {
return this.left.interpreter(context) + this.right.interpreter(context);
}

}

package interpreter;

public class SubtractNonterminalExpression extends AbstractExpression {
private final AbstractExpression left;
private final AbstractExpression right;

public SubtractNonterminalExpression(final AbstractExpression left, final AbstractExpression right) {
this.left = left;
this.right = right;
}

@Override
public int interpreter(final Context context) {
return this.left.interpreter(context) - this.right.interpreter(context);
}
}

package interpreter;

public class TerminalExpression extends AbstractExpression {
private final int i;

public TerminalExpression(final int i) {
this.i = i;
}

@Override
public int interpreter(final Context context) {
return this.i;
}

}

package interpreter;

import flyweight.Flyweight;
import flyweight.FlyweightFactory;
import flyweight.UnsharedFlyweight;

public class Client {
public static void main(String[] args) {
// TODO Auto-generated method stub
//a+b-c
final Context context = new Context();
context.addValue("a", 7);
context.addValue("b", 8);
context.addValue("c", 2);
final AddNonterminalExpression addValue = new AddNonterminalExpression
(new TerminalExpression(context.getValue("a")),  new TerminalExpression(context.getValue("b")));
final SubtractNonterminalExpression subtractValue = new SubtractNonterminalExpression
(addValue,  new TerminalExpression(context.getValue("c")));
System.out.println(subtractValue.interpreter(context));
}
}

解释器模式的优缺点：


解释器模式的应用场景和注意事项：