价值联想的关键 [英] Key to Value associations

问题描述

我想要做的是是创建汽车，为每辆创建的汽车指定一个名称。

What I am trying to do is create cars, assign a name to each car created.

以下是我的工作：

//.....codes

 public class Cars {

        Map<String, Vehicle> vehicleNames = new HashMap <String, Vehicle>();
        Car car = new Car();
        private void execute(String[] instructions)
        {

           boolean blnExists =vehicleNames.containsKey(instructions[1]);
           System.out.println("Exists? : " + blnExists); 

             if (blnExists){
               if (instructions[1].equals("build")){
                   car.makeVisible();
                  }
              }
              else {
                  System.out.println("Does not exist yet!");
              }

//more codes.......

我面临的问题：

程序编译并正常运行，汽车名称正在我想要的存储在HashMap中。但是创建的汽车似乎与他们各自的名字无关。

The program compiles and works fine, car names are being stored in the HashMap as I wanted. But the cars created don't seem to be associated to their respective names.

推荐答案

• 首先，您要区分创建新车的命令（汽车名称）和对现有汽车执行操作的命令（ carname action ）。

  • First, you want to distinguish between a command to create a new car (car name) and a command to perform an action on an existing car (carname action).

    如果是汽车名称命令，请尝试从地图中取车。如果找不到，请创建汽车并添加到地图。

    If it's a car name command, try to fetch the car from the map. If it's not found, create the car and add to map.

    如果是 carname action 命令，尝试从地图上取车。如果找不到，则显示错误消息。如果找到了，请对其执行操作。

    If it's a carname action command, try to fetch the car from the map. If it's not found, display an error message. If it's found, perform the action on it.

    这是建议的逻辑工作方式：

    Here's a suggested way to make your logic work :

    if (instructions[0].equals("car")) {
        Vehicle v = vehicleNames.get(instructions[1]);
        if (v == null) {
            // put here the code that adds a vehicle to the map
        } else {
            // display a message that the vehicle already exists
        }
    } else {
        Vehicle v = vehicleNames.get(instructions[0]);
        if (v == null) {
            // display a message that car was not found
        } else {
            // perform an action on existing car. For example :
            if (instructions[1].equals("build") {
                v.makeVisible();
            }
        }
    }
    

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