class SubData {
    Map<String, Object> map = new HashMap<String, Object>();
    public void set(String key, Object value) {
        map.put(key, value);
    }
    public Object get(String key) {
        map.get(key);
    }
    public boolean contains(String key) {
        return map.containsKey(key);
    }
}

A a = new A();

SubData b = new SubData();
b.set("xxx", a.getXXX());
b.set("yyy", a.getYYY());

SubData c = new SubData();
c.set("zzz", a.getXXX());

if (b.contains("xxx")) {
    System.out.println(b.get("xxx"));
}

------解决方案--------------------
这个设计本身就有问题。。。