Interpreter

最新推荐文章于 2025-11-27 10:55:11 发布

最新推荐文章于 2025-11-27 10:55:11 发布 · 296 阅读

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本文详细介绍了如何使用Java实现一个简单的表达式解析器，包括常量、变量、加法和减法运算的解析过程。通过创建抽象基类`Expression`和具体子类如`Constant`、`Variable`、`Add`、`Minus`，实现了基本的数学表达式计算。通过`Context`类管理变量上下文，使得表达式的计算更加灵活。

Interpreter Pattern:其意图是给定一个语言，定义它的文法表示，并定义一个解释器，这个解释器使用该标识来解释语言中的句子.

Expression.java

package com.flyingh.dp.interpreter;

public abstract class Expression {
	public abstract int interpret(Context ctx);
}

Constant.java

package com.flyingh.dp.interpreter;

public class Constant extends Expression {
	private int value;

	public Constant(int value) {
		super();
		this.value = value;
	}

	@Override
	public int interpret(Context ctx) {
		// TODO Auto-generated method stub
		return value;
	}

}

Variable.java

package com.flyingh.dp.interpreter;

public class Variable extends Expression {

	@Override
	public int interpret(Context ctx) {
		// TODO Auto-generated method stub
		return ctx.lookup(this);
	}

}

Add.java

package com.flyingh.dp.interpreter;

public class Add extends Expression {
	private Expression left;
	private Expression right;

	public Add(Expression left, Expression right) {
		super();
		this.left = left;
		this.right = right;
	}

	@Override
	public int interpret(Context ctx) {
		// TODO Auto-generated method stub
		return left.interpret(ctx) + right.interpret(ctx);
	}

}

Minus.java

package com.flyingh.dp.interpreter;

public class Minus extends Expression {
	private Expression left;
	private Expression right;

	public Minus(Expression left, Expression right) {
		super();
		this.left = left;
		this.right = right;
	}

	@Override
	public int interpret(Context ctx) {
		// TODO Auto-generated method stub
		return left.interpret(ctx) - right.interpret(ctx);
	}

}

Context.java

package com.flyingh.dp.interpreter;

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

public class Context {
	private Map<Variable, Integer> map = new HashMap<Variable, Integer>();

	public int lookup(Variable var) {
		// TODO Auto-generated method stub
		int value = 0;
		try {
			value = map.get(var);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			System.out.println(var + "还没有赋值!");
		}
		return value;
	}

	public void assign(Variable var, int value) {
		map.put(var, value);
	}

}

Client.java

package com.flyingh.dp.interpreter;

public class Client {
	public static void main(String[] args) {
		Variable var1 = new Variable();
		Variable var2 = new Variable();
		Expression con = new Constant(1);
		Context ctx = new Context();
		ctx.assign(var1, 5);
		ctx.assign(var2, 8);
		Expression add = new Add(new Constant(3), var1);
		System.out.println(add.interpret(ctx));
		Expression add2 = new Add(con, var1);
		System.out.println(add2.interpret(ctx));
		System.out.println("*************");
		ctx.assign(var1, 10);
		ctx.assign(var2, 5);
		Expression minus = new Minus(var1, var2);
		System.out.println(minus.interpret(ctx));
		System.out.println(new Minus(var2, new Constant(4)).interpret(ctx));
	}
}

程序运行结果如下：