Tencent Interview

I came across stormzhang’s Tencent interview questions and decided to work through them, documenting my answers and thought process.

Topics covered:

• Android fundamentals (processes, Activities, Handler)
• Screen density and resource qualifiers
• Thread synchronization in Java
• System design (resumable downloads, network architecture)

Interview questions:

1. How to draw a stamp pattern
2. How to implement text stroke and shadow effects
3. Can different Activities of the same app run in separate processes? If so, give an example.
4. What thread synchronization mechanisms exist in Java? Give examples.
5. Explain Handler, Looper, and HandlerThread.
6. What do dp, dip, dpi, px, sp mean? How are they converted? What do layout-sw600dp and layout-h600dp mean?
7. List Activity launch modes with your understanding and use cases.
8. How to design a resumable file download system.
9. XML layout: how to center two TextViews horizontally in a RelativeLayout.
10. Design a system that fetches data and images from the network and loads them into a list — draw the client architecture and analyze.

3. Can different Activities of the same app run in separate processes?

Yes. Normally all Activities in an application run in the same process. However, setting the android:process attribute on an Activity forces it to run in its own process.

Naming rules for android:process:

• Prefix with : (e.g., :first.process): creates a private process (prefixed with the app’s package name)
• Start with a lowercase letter (e.g., com.example.shared): creates a global process that other apps can also use

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<application android:icon="@drawable/icon"
             android:label="@string/app_name">
    <activity android:name=".MainActivity"
              android:process=":first.process" />
    <activity android:name=".SubActivity"
              android:process=":second.process" />
</application>

Two Activities from the same app can run in different processes yet belong to the same task — this demonstrates the power of Android’s task management. It allows isolating independent modules into separate processes, reducing coupling, without worrying about inter-process communication details. The implementation involves ActivityRecord and ProcessRecord scheduling managed by ActivityManagerService.

Reference: android:process | Android Developers Reference: Processes and threads overview | Android Developers

6. dp, dip, dpi, px, sp — Definitions and Conversion

Conversion between dp and px:

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public static int dip2px(Context context, float dipValue) {
    final float scale = context.getResources()
        .getDisplayMetrics().density;
    return (int)(dipValue * scale + 0.5f);
}

public static int px2dip(Context context, float pxValue) {
    final float scale = context.getResources()
        .getDisplayMetrics().density;
    return (int)(pxValue / scale + 0.5f);
}

Recommendation: use sp for text, dp for everything else.

Resource Directory Qualifiers

• swdp (e.g., layout-sw600dp): smallest width — the smaller of width/height. Does not change when the device orientation changes.
• wdp (e.g., layout-w600dp): current screen width — changes with orientation.
• hdp (e.g., layout-h600dp): current screen height — changes with orientation. The official docs recommend avoiding this qualifier, since scrollable content makes height less predictable than width.

References

• Tencent Interview - stormzhang
• android:process | Android Developers
• Processes and threads overview | Android Developers