高效，干净地处理此问题的最佳方法是让foo返回对象的holder类。
abstract class Holder<T> { private final T object; protected Holder(T object) { this.object = object; } public T get() { return object; } public abstract void doSomething();}public Holder foo(int opt) { if (opt == 0) return new Holder<String>("") { public void doSomething() { } }; else if (opt == 1) return new Holder<Integer>(1) { public void doSomething() { } }; else if (opt == 2) return new Holder<Double>(1.0) { public void doSomething() { } }; // many more}public static void main(String... args) throws IOException { Holder h = foo(x); //x is a value obtained during runtime, e.g. from user input //now I want to call doSomething method h.doSomething();}
