E

1525415182

tags: Design

让一个class 是 singleton

```

/*

Singleton is a most widely used design pattern.

If a class has and only has one instance at every moment,

we call this design as singleton.

For example, for class Mouse (not a animal mouse), we should design it in singleton.

You job is to implement a getInstance method for given class,

return the same instance of this class every time you call this method.

Example

In Java:

A a = A.getInstance();

A b = A.getInstance();

a should equal to b.

Challenge

If we call getInstance concurrently, can you make sure your code could run correctly?

Tags Expand

LintCode Copyright OO Design

*/

class Solution {

public static Solution instance = null;

public static Solution getInstance() {

if (instance == null) {

instance = new Solution();

}

return instance;

}

};

// Thread safe:

class Solution {

public static Solution solution = null;

/**

* @return: The same instance of this class every time

*/

public static Solution getInstance() {

if (solution == null) {

synchronized (Solution.class) {

// Double check

if (solution == null) {

solution = new Solution();

}

}

}

return solution;

}

};

```