How Launcher decides which app icon to place in launcher?

I have a very naive question. I've written a program which lists down all the installed applications in my Android OS [I've got total 339 in my case]. But in the Launcher [In my case TouchWiz Home] only 148 application Icons are shown.

My Question is: How does the launcher[TouchWiz Home] decide which app icon to show or not in Launcher?

Solution

Launcher will show those activities that have the following intent filters declared in the app's manifest file

 <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>