You can use Process.killProcess(int pid) to kill processes that have the same UID with your App.
You can use ActivityManager.killBackgroundProcesses(String packageName),with KILL_BACKGROUND_PROCESSES permission in your manifest(for API >= 8) or ActivityManager.restartPackage (String packageName)(for API < 8) to kill specified process,except of forground process.
So if you would to kill all other processes when your program is foreground process,you would to use ActivityManager.killBackgroundProcesses or ActivityManager.restartPackage:
List<ApplicationInfo> packages;
PackageManager pm;
pm = getPackageManager();
//get a list of installed apps.
packages = pm.getInstalledApplications(0);
ActivityManager mActivityManager = (ActivityManager)context.getSystemService(Context.ACTIVITY_SERVICE);
for (ApplicationInfo packageInfo : packages) {
if((packageInfo.flags & ApplicationInfo.FLAG_SYSTEM)==1)continue;
if(packageInfo.packageName.equals("mypackage")) continue;
mActivityManager.killBackgroundProcesses(packageInfo.packageName);
}
In above snippet code,each process will be killed unless it be process of your App or system process.