[如何判断某个对象是否继承自某类？ How to determine an object's class (in Java)?] http://stackoverflow.com/questions/541749/how-to-determine-an-objects-class-in-java #tags: java

IsInstanceOf.java

/**
 * Method #0：操作符（或者说关键字）instanceof
 * object 是 C 的实例吗？
 */
if (object instanceof C)
    ;

/**
 * Method #1: isInstance(Object object)
 * Tests whether the given object can be cast to the class represented by this Class.
 * This is the runtime version of the instanceof operator.
 * 
 * @return true if object can be cast to the type represented by this Class;
 *         false if object is null or cannot be cast.
 *
 * 方法 isInstance() 和操作符 instanceof 作用一致。
 * object 是 C 的实例吗？阅读顺序是反的，应该是为了方便定义 API 吧。
 * 而 instanceof 更符合阅读的顺序。
 */
if (C.class.isInstance(object))
    ;

/**
 * 向上转型（Upcasting）：从导出类转型为基类。
 * 向上转型总是安全的，因为导出类是基类的一个超集。《Thinking in Java》7.7.1
 */ 
    
// Method #2
/**
 * getClass(): Returns the unique instance of Class that represents this object's class. 
 * may throw NullPointerException
 */
if (obj.getClass().equals(C.class))
    ;

// Method #3
/**
 * isAssignableFrom(Class<?> c): Can c be assigned to this class? For example,
 * 
 * String can be assigned to Object (by an upcast), however, 
 * an Object cannot be assigned to a String as a potentially
 * exception throwing downcast would be necessary. Similarly for interfaces,
 * 
 * a class that implements (or an interface that extends) another
 * can be assigned to its parent, but not vice-versa（反之亦然）.
 * 
 * All Classes may assign to themselves.
 * Classes for primitive types may not assign to each other.
 */
if (C.class.isAssignableFrom(obj.getClass()))
    ;

/** null is not an instance of any type, but it can be cast to any type. */

// Method #4
try {
    C c = (C) obj;
    // No exception: obj is of type C or IT MIGHT BE NULL!
} catch (ClassCastException e) {
}

// Method #5
try {
    C c = C.class.cast(obj);
    // No exception: obj is of type C or IT MIGHT BE NULL!
} catch (ClassCastException e) {
}