ArrayList<String> fontNames = new ArrayList<String>();
File temp = new File("/system/fonts/");
String fontSuffix = ".ttf";

for(File font : temp.listFiles()) {
    String fontName = font.getName();
    if(fontName.endsWith(fontSuffix)) {
        fontNames.add(fontName.subSequence(0,fontName.lastIndexOf(fontSuffix)).toString());
    }
}