泛型在Java中的应用非常广泛,最常见则是在集合容器中,先看下基础用法:
public class Generic01 {
public static void main(String[] args) {
Map map = new HashMap<>() ;
map.put(88,"hello") ;
// map.put("99","world") ; 输入编译错误
String value = map.get(88) ;
// Integer value = map.get(88) ; 输出编译错误
System.out.println("value:"+value);
}
}
泛型即可以理解为把数据类型作为参数,即参数化类型
首先设计一个简单的顶层接口,只定义一个callBack方法,和对出入参数的简单逻辑设定
/**
* 基础接口设计
* @param 返参类型
* @param 入参类型
*/
interface CallBack {
/**
* 回调方法:V 方法入参 ,R 方法返回值
*/
R callBack (V v) ;
}
为了实现具体的业务,再基于顶层接口向下做扩展,
这里声明两个扩展接口,作为具体业务类的接口
/**
* 扩展接口设计01
*/
interface ExtCallBack01>
extends CallBack> {
@Override
Integer callBack (List list) ;
}
/**
* 扩展接口设计01
*/
interface ExtCallBack02>
extends CallBack> {
@Override
Boolean callBack (Map map) ;
}
可以通过扩展接口去设计具体的业务类,提高程序的灵活可扩展性:
public class Generic02 {
public static void main(String[] args) {
new ExtCallBack01>(){
@Override
public Integer callBack(List list) {
list.add("hello");
return list.size();
}
};
new ExtCallBack02> (){
@Override
public Boolean callBack(Map map) {
map.put("Fire",119L) ;
return map.size()>0 ;
}
} ;
}
}
反射机制可以在程序运行时获取类的完整结构信息,并且可以动态的操作属性和方法等。
API之Class对象
public static void main(String[] args) throws Exception {
// Class对象回去
User user1 = new User(1,"name01") ;
//方式一
Class userClass1 = user1.getClass() ;
//方式二
Class userClass2 = Class.forName("com.java.reflect.User");
//方式三
Class userClass3 = User.class ;
System.out.println(User.class.getName());
System.out.println("userClass1==userClass2?"+(userClass1==userClass2));
System.out.println("userClass2==userClass3?"+(userClass2==userClass3));
// 类型创建和判断
Object object = User.class.newInstance() ;
System.out.println("类型:"+(object instanceof User));
System.out.println("类型:"+(userClass3.isInstance(user1)));
}
API之Constructor构造器
public static void main(String[] args) throws Exception {
Class userClass = User.class ;
Constructor[] userConArr = userClass.getConstructors();
printCon(userConArr);
Constructor privateCon = userClass.getDeclaredConstructor(Integer.class);
System.out.println(privateCon);
userConArr = userClass.getDeclaredConstructors();
printCon(userConArr);
Constructor pubCon = userClass.getConstructor(Integer.class,String.class);
Object pubUser = pubCon.newInstance(1,"hello") ;
// 调用私有构造方法创建对象
Constructor priCon = userClass.getDeclaredConstructor(Integer.class);
// 忽略private权限修饰符
priCon.setAccessible(Boolean.TRUE);
Object priUser = priCon.newInstance(2) ;
System.out.println(pubUser+"\n"+priUser);
}
public static void printCon (Constructor[] constructors){
for (Constructor constructor:constructors){
System.out.println(constructor);
}
}
API之Field属性
public static void main(String[] args) throws Exception {
Class userClass = User.class ;
// 获取公共字段
Field[] pubArr = userClass.getFields() ;
printField(pubArr);
// 获取全部字段
Field[] fieldArr = userClass.getDeclaredFields() ;
printField(fieldArr);
// 获取指定字段
Field emailField = userClass.getField("email") ;
Field nameField = userClass.getDeclaredField("name") ;
printField(new Field[]{emailField,nameField});
// 创建对象并操作属性
Object userObj = userClass.newInstance() ;
nameField.setAccessible(Boolean.TRUE);
nameField.set(userObj,"world");
emailField.set(userObj,"[email protected]");
System.out.println("userObj:"+userObj);
}
/**
* 打印成员变量信息
*/
public static void printField (Field[] fields){
for (Field field : fields){
System.out.println("声明:"+field);
UserAnno userAnno = field.getAnnotation(UserAnno.class) ;
System.out.println("注解:"+userAnno.desc());
String fieldName = field.getName() ;
System.out.println("名称:"+fieldName);
Type type = field.getGenericType() ;
System.out.println("类型:"+type);
}
}
API之Method方法
public static void main(String[] args) throws Exception {
Class userClass = User.class ;
// 获取所有公共方法[包括父类和Object类方法]
Method[] pubMethods = userClass.getMethods() ;
printMethod(pubMethods);
// 获取全部方法
Method[] allMethods = userClass.getDeclaredMethods() ;
printMethod(allMethods);
// 获取指定方法
Method method = userClass.getMethod("parName",String.class) ;
printMethod(new Method[]{method});
// 调用方法
Object userObj = userClass.newInstance() ;
Method setId = userClass.getDeclaredMethod("setId", Integer.class);
setId.invoke(userObj,99) ;
Method setName = userClass.getDeclaredMethod("setName", String.class);
setName.invoke(userObj,"java") ;
Method sayHi = userClass.getDeclaredMethod("sayHi", String.class);
sayHi.setAccessible(Boolean.TRUE);
sayHi.invoke(userObj,"c++");
System.out.println(userObj);
}
/**
* 打印方法信息
*/
public static void printMethod (Method[] methods){
for (Method method : methods){
System.out.println("定义:"+method);
System.out.println("命名:"+method.getName());
UserAnno userAnno = method.getAnnotation(UserAnno.class) ;
if (userAnno != null){
System.out.println("注解:"+userAnno.desc());
}
Type[] paramTypeArr = method.getParameterTypes();
for (int i=0 ; i< paramTypeArr.length; i++){
System.out.print("参数"+(i+1)+"类型:"+paramTypeArr[i]+" ; ");
}
System.out.println("参数个数:"+method.getParameterCount());
}
}