I searched Stack Overflow for this question and many of the result doesn't work or is too verbose.

Hence I post it here for my future reference.

/**
 * Hides the soft keyboard
 */
public void hideSoftKeyboard() {
    if(getCurrentFocus()!=null) {
        InputMethodManager inputMethodManager = (InputMethodManager) getSystemService(INPUT_METHOD_SERVICE);
        inputMethodManager.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(), 0);
    }
}

/**
 * Shows the soft keyboard
 */
public void showSoftKeyboard(View view) {
    InputMethodManager inputMethodManager = (InputMethodManager) getSystemService(INPUT_METHOD_SERVICE);
    view.requestFocus();
    inputMethodManager.showSoftInput(view, 0);
}

source : http://stackoverflow.com/questions/18977187/how-to-hide-soft-keyboard-when-activity-starts