Java Class类

Class

/**
 * Instances of the class Class represent classes and interfaces in a running Java application.
 * 
 * Type parameters: <T> – the type of the class modeled by this Class object. For example, the type of String.class is Class<String>. Use Class<?> if the class being modeled is unknown.
 */
public final class Class<T> implements java.io.Serializable,
                              GenericDeclaration, Type, AnnotatedElement {}

Methods

isAssignableFrom()

/**
 * Determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface of, 
 * the class or interface represented by the specified Class parameter
 * Params: cls – the Class object to be checked
 * Returns: the boolean value indicating whether objects of the type cls can be assigned to objects of this class
 * 
 * X.class.isAssignableFrom(cls) ==> 判断 cls 类型的对象是否为 X 类型的实例
 * 即判断 X 与 cls 所属的类/接口是否相同，或者 X 是 cls 的父类/父接口
 */
public native boolean isAssignableFrom(Class<?> cls);

示例：

// public final class String implements CharSequence {}
Class<String> stringClass = String.class;
Class<CharSequence> charSequenceClass = CharSequence.class;

boolean b = charSequenceClass.isAssignableFrom(stringClass); // true
boolean b2 = stringClass.isAssignableFrom(charSequenceClass); // false

isInstance()

/**
 * Determines if the specified Object is assignment-compatible with the object represented by this Class.
 * Params: obj – the object to check
 * Returns: true if obj is an instance of this class
 */
public native boolean isInstance(Object obj);

示例：

/*
 * X.class.isInstance(obj) ==> 判断 对象obj 是否可以作为X类的实例
 * 等价：obj instanceof X 
 * 关键字 instanceof 更简洁，isInstance() 更灵活
 */

其他

类名.class vs 对象.getCalss()

public toString() {
    return getClass().getName() +"@" + Integer.toHexString(hashCode());
}