1
Intent intent = new Intent(MainActivity.this, SecondActivity.class);
2
startActivity(intent);

1
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("https://www.baidu.com"));
2
startActivity(intent);

1
public class MainActivity extends AppCompatActivity {
2
    @Override
3
    protected void onCreate(Bundle savedInstanceState) {
4
        super.onCreate(savedInstanceState);
5
        setContentView(R.layout.activity_main);
6

7
        Button btn1 = findViewById(R.id.btn1);
8
        Button btn2 = findViewById(R.id.btn2);
9

10
        btn1.setOnClickListener(new View.OnClickListener() {
11
            @Override
12
            public void onClick(View v) {
13
                Toast.makeText(MainActivity.this, "欢迎进入考试系统", Toast.LENGTH_SHORT).show();
14
            }
15
        });
16

17
        btn2.setOnClickListener(new View.OnClickListener() {
18
            @Override
19
            public void onClick(View v) {
20
                Intent intent = new Intent(MainActivity.this, SecondActivity.class);
21
                intent.putExtra("number", "20230001");
22
                intent.putExtra("name", "张三");
23
                intent.putExtra("age", 20);
24
                startActivity(intent);
25
            }
26
        });
27
    }
28
}

1
public class SecondActivity extends AppCompatActivity {
2
    @Override
3
    protected void onCreate(Bundle savedInstanceState) {
4
        super.onCreate(savedInstanceState);
5
        setContentView(R.layout.activity_second);
6

7
        TextView tvShow = findViewById(R.id.tv_show);
8

9
        Intent intent = getIntent();
10
        String number = intent.getStringExtra("number");
11
        String name = intent.getStringExtra("name");
12
        int age = intent.getIntExtra("age", 0);
13

14
        tvShow.setText("学号：" + number + "\n姓名：" + name + "\n年龄：" + age);
15
    }
16
}

1
public class MainActivity extends AppCompatActivity {
2
    @Override
3
    protected void onCreate(Bundle savedInstanceState) {
4
        super.onCreate(savedInstanceState);
5
        setContentView(R.layout.ss);  // 布局文件 ss.xml
6

7
        final EditText ed1 = findViewById(R.id.ed_number1);
8
        final EditText ed2 = findViewById(R.id.ed_number2);
9
        final TextView tv  = findViewById(R.id.tv);
10
        Button btn = findViewById(R.id.btn);
11

12
        btn.setOnClickListener(new View.OnClickListener() {
13
            @Override
14
            public void onClick(View v) {
15
                String s1 = ed1.getText().toString();
16
                String s2 = ed2.getText().toString();
17
                if (s1.isEmpty() || s2.isEmpty()) {
18
                    tv.setText("请输入两个数字");
19
                    return;
20
                }
21
                double num1 = Double.parseDouble(s1);
22
                double num2 = Double.parseDouble(s2);
23
                double result = num1 * num2;
24
                tv.setText("结果：" + result);
25
            }
26
        });
27
    }
28
}

1
public class MyHelper extends SQLiteOpenHelper {
2

3
    public MyHelper(Context context) {
4
        super(context, "library.db", null, 1);
5
    }
6

7
    @Override
8
    public void onCreate(SQLiteDatabase db) {
9
        String createTable = "create table book("
10
                + "id integer primary key,"
11
                + "name text,"
12
                + "price real)";
13
        db.execSQL(createTable);
14

15
        // 插入两条记录
16
        db.execSQL("insert into book(id, name, price) values(?, ?, ?)",
17
                new Object[]{1, "钢铁是怎样炼成的", 38.5});
18
        db.execSQL("insert into book(id, name, price) values(?, ?, ?)",
19
                new Object[]{2, "告别内耗", 59.8});
20
    }
21

22
    @Override
23
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
24
        // 升级时的处理
25
    }
26
}

1
MyHelper helper = new MyHelper(this);
2
SQLiteDatabase db = helper.getWritableDatabase();  // 触发 onCreate

1
public class MainActivity extends Activity {
2
    private MyReceiver receiver;
3

4
    protected void onCreate(Bundle savedInstanceState) {
5
        super.onCreate(savedInstanceState);
6
        setContentView(R.layout.activity_main);
7
        receiver = new MyReceiver();
8
        IntentFilter filter = new IntentFilter("YourAction");
9
        registerReceiver(receiver, filter);          // 注册广播监听
10
    }
11

12
    public void myRegist(View view) {
13
        Intent intent = new Intent("YourAction");
14
        Bundle bundle = new Bundle();
15
        bundle.putString("way", "我的注册方式");      // 放入 String
16
        bundle.putDouble("number", 10.8);            // 放入 double
17
        intent.putExtras(bundle);
18
        sendBroadcast(intent);                        // 发送广播
19
    }
20

21
    protected void onDestroy() {
22
        super.onDestroy();
23
        unregisterReceiver(receiver);                 // 注销广播
24
    }
25
}

1
public class MyReceiver extends BroadcastReceiver {
2
    public void onReceive(Context context, Intent intent) {
3
        if (intent.getAction().equals("YourAction"))
4
        // 注释1：判断接收到的广播 Action 是否为 "YourAction"，过滤目标广播
5
        {
6
            String data = intent.getStringExtra("class");
7
            // 注释2：从 intent 中取出键为 "class" 的 String 数据
8

9
            Log.d("MyReceiver", "我的班级是：" + data);
10
            // 注释3：在 Logcat 中以 debug 级别打印取出的数据，便于调试
11

12
            Bundle bundle = new Bundle();
13
            bundle.putString("order", "尽快报到");
14
            // 注释4：创建 Bundle 并放入键 "order"、值 "尽快报到" 的字符串数据
15

16
            setResultExtras(bundle);
17
            // 注释5：将 bundle 作为有序广播的结果数据回传给下一个接收者或发送者
18
        }
19
    }
20
}

1
public class MainActivity extends Activity {
2
    protected void onCreate(Bundle savedInstanceState) {
3
        super.onCreate(savedInstanceState);
4
        setContentView(R.layout.activity_main);
5

6
        findViewById(R.id.button1).setOnClickListener(new OnClickListener() {  // 1. 添加动作监听
7
            public void onClick(View arg0) {
8
                Intent intent = new Intent(MainActivity.this, SecondActivity.class);  // 2. 跳转
9
                intent.putExtra("id", 110);            // 3. 添加 int 类型数据
10
                intent.putExtra("scores", 98.5);       // 4. 添加 double 类型数据
11
                startActivity(intent);                  // 5. 传递并启动 Activity
12
            }
13
        });
14
    }
15
}

1
public class MyHelper extends SQLiteOpenHelper {
2

3
    public MyHelper(Context context) {
4
        super(context, "courseSelect.db", null, 1);
5
    }
6
    // 方法1：构造方法。调用父类 SQLiteOpenHelper 的构造，指定数据库名为
7
    // "courseSelect.db"，使用默认游标工厂(null)，数据库版本号为 1。
8

9
    @Override
10
    public void onCreate(SQLiteDatabase db) {
11
        String createTable = "create table student"
12
            + "(id integer primary key autoincrement,name text,number text,gender text,age integer)";
13
        db.execSQL(createTable);
14
    }
15
    // 方法2：当数据库**首次创建**时被调用。
16
    // 通过 SQL 语句创建 student 表，包含 id（主键自增）、name、number、gender、age 五个字段。
17

18
    @Override
19
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
20
        // TODO Auto-generated method stub
21
    }
22
    // 方法3：当数据库**版本升级**（构造方法中传入的版本号高于旧版本）时被调用，
23
    // 用于对旧表进行结构升级（如删除旧表、新建表、添加字段等迁移操作）。
24
}

1
public class MyService extends Service {
2
    public IBinder onBind(Intent arg0) { return null; }
3

4
    public void onCreate() {
5
        super.onCreate();
6
        Log.d("Service", "onCreate: 服务已创建");
7
    }
8

9
    public int onStartCommand(Intent intent, int flags, int startId) {
10
        Log.d("Service", "onStartCommand: 服务正在运行");
11
        return START_STICKY;
12
    }
13

14
    public void onDestroy() {
15
        super.onDestroy();
16
        Log.d("Service", "onDestroy: 服务已停止");
17
    }
18
}

1
onCreate: 服务已创建
2
onStartCommand: 服务正在运行

1
onStartCommand: 服务正在运行

1
<service android:name=".MyService" />