Android：使用全局对象而不是创建新对象

Question

I have a class A in my Android app where I have some methods. Those methods are public and used in other classes (B, C, D, E, F ...).

Is there a possibility to create only once the object from the class A and then use it in the other classes or i have to create new object in each classe.

Actually I have to do in each classe (B, C, D, E, F ...)

A a = new A();
a.xxxx;

It will be great if I can create only once the object a and then call it in my other classes.

thank you.

Answer 1

Use a singleton pattern. It allows you to use the same instance across classes:

http://www.javabeginner.com/learn-java/java-singleton-design-pattern

Answer 2

class A{
    static A a;
    static{
          a = new A();
    }
}

In every other class use

A.a to get the object and call respective methods as
A.a.xxxx()

Answer 3

Use static methods's analogy to do this.

For example:

public class Helper{
    public static void doSomething(){
        //do something here
    }
}

Now in your other classes, use the above method as below:

Helper.doSomething();

Or Singleton pattern would be an alternate too.

Answer 4

Instead of that why don't you make those methods static or consider single instance pattern if there are no states involved..

how to use static methods and singleton pattern

Answer 5

I see the following 3 possibilities:

1. If these are just "normal" helper methods you may also just do

class B extends A

and inherit the methods of A into B,C,D,E,....

2. However if you need internal memory of class A which is global to all other classes or their instances of B,C,D then may use the static pattern like

class A{

static int myGlobalIntVariable; //which is accessible from everywhere 
static void myHelperMethod1() {

}

or 3. Also you may use singleton as mentioned above which creates an instance that you use everywhere.

Just as a remark, you may use singleton or static pattern depending what you prefer when accessing the methods.

For static patter you have to call them like:

A.myHelperMethod();

and for singleton you have to do:

A.getSingleton().myHelperMethod1();  or A.singleton.myHelperMethod1()

if you have defined a variable called singleton within Class A

Which one to use really depends on your needs and taste :-)