Android[高级教程] 设计模式之七 单例模式
单例模式也是我最喜欢的模式，因为不管你创建多少个对象，当前对象在内存中只存在一份实例，而且像Android中对数据库的操作，对HTTP的请求都可以用单例模式来实现，而且效率也会提升不少。这里我们就对《西游记》里的主人公唐僧来实现单例模式呢：
[java] <pre name="code" class="java">public class Tangseng {
private static Tangseng tangseng;
Tangseng() {
// TODO Auto-generated constructor stub
}
public Tangseng getInstance() {
if (tangseng == null) {
tangseng = new Tangseng();
}
return tangseng;
}
}
<pre name="code" class="java">public class Tangseng {
private static Tangseng tangseng;
Tangseng() {
// TODO Auto-generated constructor stub
}
public Tangseng getInstance() {
if (tangseng == null) {
tangseng = new Tangseng();
}
return tangseng;
}
}
就简单的几行代码，我们就实现了单例模式，以后调用的时候不管你new多少个对象，内存中只有一个。
在Android中调用一下看一下呢，
[java] public class XiyoujiActivity extends Activity {
private ListView listView;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
listView = (ListView) findViewById(R.id.listView1);
ArrayList<String> lists = new ArrayList<String>();
lists.add(new Tangseng().getInstance().toString());
lists.add(new Tangseng().getInstance().toString());
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.易做图_list_item_1, lists);
listView.setAdapter(adapter);
}
}
public class XiyoujiActivity extends Activity {
private ListView listView;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
listView = (ListView) findViewById(R.id.listView1);
ArrayList<String> lists = new ArrayList<String>();
lists.add(new Tangseng().getInstance().toString());
lists.add(new Tangseng().getInstance().toString());
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.易做图_list_item_1, lists);
listView.setAdapter(adapter);
}
}显示结果：
大家从图上应该能看出来，不管我new了多少个唐僧的类，它的内存地址是同一个，这就是单例模式的特性，因为一般我们都将实现单例模式的类静态化，静态化是什么意思呢？静态化就是将方法变成静态方法，JAVA中对于静态方法是可以直接调用的，不需要new出来的。接下来我们再重构一下：
[java] public class Tangseng {
private static Tangseng tangseng;
private Tangseng() {
// TODO Auto-generated constructor stub
}
public static Tangseng getInstance() {
if (tangseng == null) {
tangseng = new Tangseng();
}
return tangseng;
}
}
public class Tangseng {
private static Tangseng tangseng;
private Tangseng() {
// TODO Auto-generated constructor stub
}
public static Tangseng getInstance() {
if (tangseng == null) {
tangseng = new Tangseng();
}
return tangseng;
}
}其实也没多大改动，只是在getInstance方法前面加了个static 名称，这样这个方法就实现了静态方法，静态方法有什么好处呢？在Android中对于每个对象的生命周期都有很严格的规定，例如当前的Activity被另一个Activity覆盖，如果Android运行内存不够的话，前面的Activity就会被回收掉，但如果这个方法实现了static，一般是不会被回收的，这样我们就提高的代码的运行效率。接下来就我们再改一下调用方式呢：
[java] public class XiyoujiActivity extends Activity {
private ListView listView;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
listView = (ListView) findViewById(R.id.listView1);
ArrayList<String> lists = new ArrayList<String>();
lists.add(Tangseng.getInstance().toString());
lists.add(Tangseng.getInstance().toString());
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.易做图_list_item_1, lists);
listView.setAdapter(adapter);
}
}
public class XiyoujiActivity extends Activity {
private ListView listView;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
listView = (ListView) findViewById(R.id.listView1);
ArrayList<String> lists = new ArrayList<String>();
lists.add(T
补充：移动开发 , Android ,
