I had to call this to make it work:

1. self.setup();

This code works perfectly for me on Eclipse (Android 2.3.6), with GBTab as inner class of the Processing PApplet

2. class GBTab extends TabHost { 
     private PApplet parent;
3.   TabHost self;
4.   TabWidget tab1, tab2;
5.   LinearLayout layout;
6. 
   
7.   public GBTab(PApplet _parent) {
8. 
   
9.     super(_parent.getApplicationContext());
10.     parent = _parent;
11.     init();
12.   }
13.   public void init() {
14.     println("GBTab init");
15.     self = this;
16.     self.setId(android.R.id.tabhost);
17.     TabWidget widget = new TabWidget(parent);
18.     widget.setId(android.R.id.tabs);
19.     FrameLayout content = new FrameLayout(parent);
20.     content.setId(android.R.id.tabcontent);
21.     layout = new LinearLayout(parent);
22.     layout.setOrientation(LinearLayout.VERTICAL);
23.     layout.addView(widget);
24.     layout.addView(content);
25.     self.addView(layout);
26. 
    
27.     self.setup();
28.     TabSpec settingsSpec = self.newTabSpec("SETTINGS").setContent(
29. 
    
30.     new TabContentFactory() {
31.       public View createTabContent(String tag) {
32.         TextView tv = new TextView(parent);
33.         tv.setText("WORKS!");
34.         return tv;
35.       }
36.     }
37.     )
38.       .setIndicator("SETTINGS");
39. 
    
40.     self.addTab(settingsSpec);
41.     TabSpec presetsSpec = self.newTabSpec("PRESETS")
42.       .setContent(new TabContentFactory() {
43. 
    
44.         public View createTabContent(String tag) {
45.           TextView tv = new TextView(parent);
46.           tv.setText("WORKS!");
47.           return tv;
48.         }
49.       }
50.     )
51.       .setIndicator("PRESETS");
52. 
    
53.     self.addTab(presetsSpec);
54.     self.setCurrentTab(0);
55.     self.setSoundEffectsEnabled(false);
56.     //setContentView(self);
57.     parent.runOnUiThread(new Runnable() {
58.       public void run() {
59.         parent.addContentView(self, new ViewGroup.LayoutParams(
60.         ViewGroup.LayoutParams.FILL_PARENT, 
61.         ViewGroup.LayoutParams.FILL_PARENT));
62.       }
63.     }
64.     );
65.   }
66. 
    
67.   public void close() {
68.     layout.removeAllViewsInLayout();
69.     self.setVisibility(View.GONE);
70.     ((ViewManager) self.getParent()).removeView(self);
71.     parent.runOnUiThread(new Runnable() {
72.       public void run() {
73.         layout.removeAllViews();
74.         layout.setVisibility(View.GONE);
75.       }
76.     }
77.     );
78.   }
79. }

You'll have to create an XML file inside res/layout with this content:

1. <?xml version="1.0" encoding="utf-8"?>

   <TabHost xmlns:android="http://schemas.android.com/apk/res/android"

       android:id="@+id/tabhost"

       android:layout_width="fill_parent"

       android:layout_height="fill_parent">

      

           <TabWidget

               android:id="@+id/tabs"

               android:layout_width="fill_parent"

               android:layout_height="wrap_content" />

           <FrameLayout

               android:id="@+id/tabcontent"

               android:layout_width="fill_parent"

               android:layout_height="fill_parent"/>

    

   </TabHost>