通過名稱獲取實例變量

Question

我有兩個班，A和B。

B包含A的實例。我想按其名稱從B返回A的實例：

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;
            }
        }
    }
}

是否可以執行代碼注釋中描述的操作？ 提前致謝。

Answer 1

這是為將鍵（在這種情況下為字符串）與對象配對而創建的哈希圖的多少

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);
    }
}

筆記

• 在Java 7+中，您不需要添加第二個<String,A> ，菱形推斷就可以了，因此在Java 7或更高版本中，它將是：

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