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：
