java - 访问对象数组项，java

Question

我使用数组语句创建了一个数字对象，并且可以在创建类时打印类中传递的值，但是当我尝试从类外部(monopolygame 类)检索元素值时，它不会识别引用 - 我怎样才能正确引用它？

public class monopolygame {

    public static void main(String[] args) {

        //set up array of 18 objects    
        property properties[] = new property[18];

        //create 18 property objects and populate array
        properties[0] = new property("a","available",400,500);//create property
        properties[1] = new property("b","available",400,500);//create property 
        properties[2] = new property("c","available",200,300);//create property 
        properties[3] = new property("d","available",100,180);//create property
        properties[4] = new property("e","available",400,700);//create property
    }
}

属性类别...

public class property
{
   public static void main(String[] args)
   {
   }

   //constructor
   public property(String propertyname, String owner, double price, double rent) 
   {
        System.out.println("Property info for " + propertyname 
                           + " - Rent : £" + rent 
                           + "Price : £" + price 
                           + "owned by :" + owner);
    }   
}

我在垄断类中使用这种引用来尝试访问数据

if (properties[2].propertyname == "available")
{
    System.out.println("avaialble");
}
else
{
    System.out.println("sold");
}

谢谢

Answer 1

您必须首先在“property”类中声明这些属性:

class property  {
    String propertyname;
    String owner;
    int    price;
    int rent;
     public Property( String somename, String owner, int price, int rent ) {
         this.propertyname = somename;
         this.owner = owner;
         this.price = price;
         this.rent = rent;
         // and so on
      }
 }

您使用的数组是 main 方法的本地数组。

要在 main 方法的范围之外访问它，您应该将其声明为 class 属性或 instance 属性，如下所示:

public class monopolygame {
    public static property properties[]; 
    public static void main(String[] args) {
    //set up array of 18 objects

    properties = new property[18];
    .....

这样你就可以用其他方法访问数组，如下所示:

    public void setUp() {
         for( property p : properties ) {
             System.out.println( p.propertyname ); // etc. 

然后你的代码:

if (properties[2].propertyname == "available")

会起作用的。

顺便说一句，Java中所有类名按照惯例都以大写开头，所以应该是:

Property 代替 property 和 MonopolyGame 代替 monopolygame