单例模式

To create a singleton, you create a class with a private constructor and a get() method. If the instance already exists, then get() simply returns the instance. If the instance does not exist yet, then get() will call the constructor to create it.

建立一个单例，可以创建一个私有的构造器，和一个get()方法，当实例已经存在的时候，get方法就返回实例，当不存在的时候就利用构造器构建。

import android.content.Context;/** * Created by wang on 16-11-15. */public class CrimeLab {    private static CrimeLab sCrimeLab;    public static CrimeLab get(Context context) {        if (sCrimeLab == null) {            sCrimeLab = new CrimeLab(context);        }        return sCrimeLab;    }    private CrimeLab(Context context) {            }}