Get instance variable by its name

Question

I have two classes, A and B.

B contains the instances of A. I want to return instance of A from B by its name:

class A
{
    public String name;

    public A (String name)
    {
        this.name = name;
    }
}

class B
{
    public A a1;
    public A a2;
    public A a3;

    public B ()
    {
        this.a1 = new A ("a1");
        this.a2 = new A ("a2");
        this.a3 = new A ("a3");
    }

    public A get_A_byName (String name)
    {
        // Is it possible to write something like this? B will always contain only instances of A
        for (A a : B.variables)
        {
            if (a.name.equals(name))
            {
                return a;
            }

            // Or in case A doesn't have a variable "name", can I get an A instance by its declared name in B?
            if (a.getClass().getName().equals(name))
            {
                return a;
            }
        }
    }
}

Is it possible to do things described in code's comments? Thanks in advance.

Answer 1

这或多或少是为了将密钥(在本例中为字符串)与对象配对而制作的散列图

class B
{
    private HashMap<String,A> theAs=new HashMap<String,A>(); //give better name


    public B ()
    {
        theAs.put("a1",new A ("a1")); //A probably doesn't need to keep its own name internally now, but have left it as its in your original code
        theAs.put("a2",new A ("a2"));
        theAs.put("a3",new A ("a3"));
    }

    public A get_A_byName (String name)
    {
        return theAs.get(name);
    }
}

笔记

• 在Java 7+中你不需要添加第二个<String,A>,钻石推理会做,所以在Java 7或更高版本中它将是:

  private HashMap<String,A> theAs=new HashMap<>();