如何在对象中存储Set / HashSet？

Question

 public HashSet<String> Red;
 public HashSet<String> Blue;
 public HashSet<String> Colors;

public Data(HashSet<String> red, HashSet<String> blue, HashSet<String> colors) {
  Red = red;
  Blue = blue;
  Colors = colors;
}

I try to store 3 Set / HashSet inside this Object. Is this way to correct way, could I acces due the object the Set/HashSet, like normal ones:

public Set<String> Red = new HashSet<String>();

Answer 1

If you are asking how to access the HashMap s inside your Data object

To access one of the three HashSets, you would create a new Data object and access the public field of choice after the Data object has been initialized:

HashSet<String> setOne = new HashSet<String>();
HashSet<String> setTwo = new HashSet<String>();
HashSet<String> setThree = new HashSet<String>();

Data d = new Data(setOne, setTwo, setThree);
d.Blue.add("this will be added to setTwo");

Normally however, you would want not to have public fields, but instead make them private and provide getter/setter methods, as this will provide encapsulation .

If you are asking whether you should refer to the interface or class

First: HashSet is a concrete class and Set is an interface. Also: The reference type decides what methods you can call upon an object. (This would be the left side of the equals sign, while the right side is the dynamic type).

In the constructor you would want to be the least specific as possible. Are you not using any special functionality of the HashSet class, you should favour referring to the Set interface, as this is much more flexible should you want to change implementation of the Data class later on - it also makes it possible for users of your class to use every class that implements Set rather than to be restricted of using the HashSet.

Do you however need special functionality of a specific class, you would of course then refer to that class.

Answer 2

如果我理解正确，您是否在问是否允许Set<String> Red = new HashSet<String>()和HashSet<String> Red = new HashSet<String>() ？