有時需要在一個class內宣告n個內部類，例項化內部類使用如下程式碼

trial("Synch", CALL_COUNT, new Immutable().new Synch());

public class Immutable { private static final long CALL_COUNT = 1000000000L; public static void main(String[] args){ trial("Synch", CALL_COUNT, new Immutable().new Synch()); trial("NotSynch", CALL_COUNT, new Immutable().new NotSynch()); } private static void trial(String msg,long count,Object obj){ System.out.println(msg + ":BEGIN"); long start_time = System.currentTimeMillis(); for(long i = 0;i<count;i++){ obj.toString(); } System.out.println(msg + ":END"); System.out.println("Elapsed time = " + (System.currentTimeMillis() - start_time) + "msec."); } class NotSynch{ private final String name="NotSynch"; public String toString(){ return "["+name+"]"; } } class Synch{ private final String name = "Synch"; public synchronized String toString(){ return "["+name+"]"; } } }