public final class Test{
		public static int totalNumber= 5 ;
		public final int id;
		public Test(){
			id = ++totalNumber;//只能在構造方法中給final變量賦值
		}
   		public static void main(String[] args) {
			Test t = new Test();
			//t.id=10;
			System.out.println(t.id);		
			final int i = 10;
			final int j;
			j = 20;
			//j = 30; //非法
    		}
}