java.lang.Class

Instances of class Class represent Java (object and class) types. Instances of this class are created only by the JVM as classes are loaded.

• public static Class forName(String) - takes string name of a class, attempts to load, link and return a Class object representing the class.
• public Object newInstance() - create and initialize new instance of class.
• public Field getField(String) - get Field object representing field of specified name.
• public Method getMethod(String, Class[]) - second parameter is used to match with argument types of the method with the given name.

  (getField/getMethod only work for public fields/methods. There are getDeclaredF/M...() methods which will get fields/methods of any access type but not inherited fields/methods. )

• Other interesting methods: getName(), getInterfaces(), getSuperclass(), getModifiers(): [public/ prot/ priv/ final/interface], getFields(), getMethods(), isInstance() - dynamic version of instanceof

  ( getFields()/getMethods() return arrays of Fields/Methods, including those that are hidden/overriden.)

The methods for examining the components of a class come in four variants. I give examples using the set of methods used to access fields. Given a Class object, one can:

• Request all the public members that are either declared in the class or inherited, using getFields().

• Request all the members that are actually declared in the current class/interface, not including inherited members, but including both public and non-public members, using getDeclaredFields().

• Request a particular public member (declared or inherited), using getField(name).

• Request a particular declared member (non-inherited but any access), using getDeclaredField(name).

Implementation of all these methods is native. Class.forName() causes the JVM to go look for the given class and creates a Class object representing the class. newInstance() causes JVM to try to allocate and initialize (ie. call no-argument constructor) an object of the type corresponding to the class, also doing checks for abstractness/interface/illegal access. getField/getMethod use the internal representation of the Class to create an instance of a Field/Method class.

Field/Method/Class classes have a getDeclaringClass() method which returns the Class object representing the class (or interface) which defines the field/method/constructor/class. In fact, they also all have getName() and getModifiers() methods.

Modifiers are represented as bits in an integer. The Modifier class has constants for the various possibilities.