这篇文章主要介绍如何使用android开发实现hello world项目，文中介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们一定要看完！
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最近开始在学android开发，这是我的第一个项目 ——hello world！
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//设置activity的布局-->res/layout/activity_main.xml
setContentView(R.layout.activity_main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}android的主activity类，activity类是android用来显示用户界面的类。
public final class R {
public static final class attr {
}
public static final class dimen {
/** Default screen margins, per the Android Design guidelines.
Customize dimensions originally defined in res/values/dimens.xml (such as
screen margins) for sw720dp devices (e.g. 10" tablets) in landscape here.
*/
public static final int activity_horizontal_margin=0x7f040000;
public static final int activity_vertical_margin=0x7f040001;
}
public static final class drawable {
public static final int ic_launcher=0x7f020000;
}
public static final class id {
public static final int action_settings=0x7f080000;
}
public static final class layout {
public static final int activity_main=0x7f030000;
}
public static final class menu {
public static final int main=0x7f070000;
}
public static final class string {
public static final int action_settings=0x7f050001;
public static final int app_name=0x7f050000;
public static final int hello_world=0x7f050002;
}
public static final class style {
/**
Base application theme, dependent on API level. This theme is replaced
by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
Theme customizations available in newer API levels can go in
res/values-vXX/styles.xml, while customizations related to
backward-compatibility can go here.
Base application theme for API 11+. This theme completely replaces
AppBaseTheme from res/values/styles.xml on API 11+ devices.
API 11 theme customizations can go here.
Base application theme for API 14+. This theme completely replaces
AppBaseTheme from BOTH res/values/styles.xml and
res/values-v11/styles.xml on API 14+ devices.
API 14 theme customizations can go here.
*/
public static final int AppBaseTheme=0x7f060000;
/** Application theme.
All customizations that are NOT specific to a particular API-level can go here.
*/
public static final int AppTheme=0x7f060001;
}
}这是R.java，这个类有eclipse自动生成，不需要开发者手动写，是用来为组件，资源注册id的，便于
在activity中找到相应资源的引用
