Java：如何访问另一个类的变量

Question

I have a class GameScreen which has an instance of a class Sprites (I have named the instance gameSprites). In Sprites there is an instance of a third class, which I have named enemies.

My question is, can I access a variable in enemies from GameScreen? Can I type gameSprites.enemies.variableName ? And can I continue that for more than two different classes?

Answer 1

If Your Variable is Private you need to have Public method to access that Variable . Suppose I have This Dummy Enemies Class of Yours

    package com;

public class Enemies {

    private final String name="HELLO";
    public final String names="This is public Variable";
    public static String name2="HELLO THIS IS STATIC";
    public Enemies(){};

    public String getName(){
        return name;
    }
}

and here in Sprites Class like your requirement i created Enemies instance

package com;

public class Sprites {

    public Sprites(){};
    Enemies enemies = new Enemies();
}

This is Dummy GameScreen Class

package com;

    public class GameScreen {
        public static void main(String...strings){
        Sprites gameSprites = new Sprites();
        System.out.println(gameSprites.enemies.names);
        String name=gameSprites.enemies.name2;// This is Highly Discouraged Approach
        System.out.println(name);
        System.out.println(gameSprites.enemies.getName());
        }
    }

and the Output When You Run This Code.

This is public Variable
HELLO THIS IS STATIC
HELLO

So What you are trying to achieve can be done for public and Static variable(This one is not encouraged to do) . For private you need to have a Public Method to access that Variable.

Answer 2

In Java world, its not really recommended. You're able to access via objectName.memberName because your member attribute is a public one. As a convention, we usually keep members private and have getters and setter through which we access the values.

And coming back your question, you can access that way to any level given that each of the members are declared public. Say, gameSprites.enemies.enemy1.enemy1Army.solder1 is also possible if enemies is public in gameSprites class, enemy1 is public in enemies class and so on.

Answer 3

This is really very basic things of any OOP language. In my opinion, you should spend some times on study those basic things, otherwise there is a good chance that you will stuck further when you proceed from this problem. However, here is an example to how to access variable of other class from another class. Accessing a variable from another class

Answer 4

It might be accessible if there is public property of class "enemies". But you are not doing it in a right way. You should make these properties private, then create public methods(getter/setter) to access the properties of those objects.