I'm a new graduate Android engineer. I recently read Effective Java and found the keyword ** static factory method **.
EffectiveJava says
Just a static method that returns an instance of the class
... apparently ...
For example, if you look at the code example of the Boolean class,
public static Boolean valueOf(boolean b) {
return b ? Boolean.TRUE : Boolean.FALSE;
}
This method converts a basic data value called boolean to a Boolean object reference.
Normally, in order for a client to get an instance of a class, it is necessary to go through a public constructor, but if you use a static factory method, you can get an instance through a static method.
By the way, although the names are similar, they are different from the factory method, which is a kind of design pattern, so be careful not to confuse them.
Since the story of the design pattern came out, I will write it as a singleton pattern.
Guarantee that only one instance of that class will be created
There is a design pattern.
As a code to realize this, in Java, you can often see the following writing style.
public class Singleton {
private static Singleton singleton = new Singleton();
private Singleton() {
}
public static Singleton getInstance() {
return singleton;
}
}
In this case, getInstance () is a static factory method. Even if you don't know about the static factory method, many people know the singleton pattern, so I think this example will give you an image.
There is also a naming convention because if each person decides the method name as much as he / she likes, it will be indistinguishable from other static methods. Generally, there are the following method names.
| Method name | role |
|---|---|
| valueOf | Returns an instance with the same value as the parameter. Type conversion. |
| of | Method name without value of valueOf |
| getInstance | Returns the instance specified by the parameter, but does not have the same value. In the case of a singleton, it takes no arguments and returns only one instance. |
| newInstance | Similar to getInstance, except that all returned instances are separate. |
| getType | Similar to getInstance, except that the factory method is in a different class than the target class. |
| newType | Similar to newInstance, except that the factory method is in a different class than the target class. |
If you have these static methods in your class, you can realize that they are static factory methods.
You can also see these methods in standard classes (such as Boolean above).
So what makes you happy with the static factory method? It will be long, so I would like to summarize it in Part 2. Up to here for this time
By Joshua Bloch Translated by Yoshiki Shibata Effective Java Second Edition
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