java 技术提升，复习，总结（二）

               java 技术提升，复习，总结（二）

 接上篇反射：

数组的反射,同样看代码理解：

int [] a1 = new int[]{1,2,3};int [] a2 = new int[4];int[][] a3 = new int[2][3];String [] a4 = new String[]{"a","b","c"};System.out.println(a1.getClass() == a2.getClass());System.out.println(a1.getClass() == a4.getClass());System.out.println(a1.getClass() == a3.getClass());System.out.println(a1.getClass().getName());System.out.println(a1.getClass().getSuperclass().getName());System.out.println(a4.getClass().getSuperclass().getName());Object aObj1 = a1;Object aObj2 = a4;//Object[] aObj3 = a1;Object[] aObj4 = a3;Object[] aObj5 = a4;System.out.println(a1);System.out.println(a4);System.out.println(Arrays.asList(a1));System.out.println(Arrays.asList(a4));printObject(a4);printObject("xyz");

private static void printObject(Object obj) {Class clazz = obj.getClass();if(clazz.isArray()){int len = Array.getLength(obj);for(int i=0;i<len;i++){System.out.println(Array.get(obj, i));}}else{System.out.println(obj);}}

4：ArrayList与HashSet

                Collection collections = new HashSet();ReflectPoint pt1 = new ReflectPoint(3,3);ReflectPoint pt2 = new ReflectPoint(5,5);ReflectPoint pt3 = new ReflectPoint(3,3);collections.add(pt1);collections.add(pt2);collections.add(pt3);collections.add(pt1);

              System.out.println(collections.size());

      public class ReflectPoint {private int x;public int y;

public ReflectPoint(int x, int y) {super();this.x = x;this.y = y;}@Overridepublic int hashCode() {final int prime = 31;int result = 1;result = prime * result + x;result = prime * result + y;return result;}@Overridepublic boolean equals(Object obj) {if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;final ReflectPoint other = (ReflectPoint) obj;if (x != other.x)return false;if (y != other.y)return false;return true;}}

5：利用反射来处理javaBean

        ReflectPoint pt1 = new ReflectPoint(3,5);        String propertyName = "x";

                Object retVal = getProperty(pt1, propertyName);System.out.println(retVal);                 Object value = 7; setProperties(pt1, propertyName, value);

private static void setProperties(Object pt1, String propertyName,Object value) throws IntrospectionException,IllegalAccessException, InvocationTargetException {PropertyDescriptor pd2 = new PropertyDescriptor(propertyName,pt1.getClass());Method methodSetX = pd2.getWriteMethod();methodSetX.invoke(pt1,value);}private static Object getProperty(Object pt1, String propertyName)throws IntrospectionException, IllegalAccessException,InvocationTargetException {/*PropertyDescriptor pd = new PropertyDescriptor(propertyName,pt1.getClass());Method methodGetX = pd.getReadMethod();Object retVal = methodGetX.invoke(pt1);*/BeanInfo beanInfo =  Introspector.getBeanInfo(pt1.getClass());PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();Object retVal = null;for(PropertyDescriptor pd : pds){if(pd.getName().equals(propertyName)){Method methodGetX = pd.getReadMethod();retVal = methodGetX.invoke(pt1);break;}}return retVal;}

使用第三方的BeanUtils工具类对javaBean进行操作方法一：//获取变量值  pt1 为javaBean对象System.out.println(BeanUtils.getProperty(pt1, "x"));//给变量设值BeanUtils.setProperty(pt1, "x", "9");System.out.println(pt1.getX());方法二：/*//java7的新特性Map map = {name:"zxx",age:18};//将map对象转成javaBean类型BeanUtils.setProperty(map, "name", "lhm");*///birthday.time 找到属性BeanUtils.setProperty(pt1, "birthday.time", "111");System.out.println(BeanUtils.getProperty(pt1, "birthday.time"));PropertyUtils.setProperty(pt1, "x", 9);System.out.println(PropertyUtils.getProperty(pt1, "x"));

</pre><pre code_snippet_id="143817" snippet_file_name="blog_20140106_11_138342" name="code" class="java">******************************************

<span style="font-size:24px;">6 注解：</span>import java.lang.reflect.Method;import javax.jws.soap.InitParam;//使用注解 并为各个属性赋值@ItcastAnnotation(annotationAttr=@MetaAnnotation("flx"),color="red",value="abc",arrayAttr={1})public class AnnotationTest {/*** @param args*/@SuppressWarnings("deprecation") //过时警告//使用带属性的注解，只有value属性时可直接赋值@ItcastAnnotation("xyz")public static void main(String[] args) throws Exception{// TODO Auto-generated method stubSystem.runFinalizersOnExit(true);if(AnnotationTest.class.isAnnotationPresent(ItcastAnnotation.class)){//检查是否使用了自定义的注解ItcastAnnotation annotation = (ItcastAnnotation)AnnotationTest.class.getAnnotation(ItcastAnnotation.class);//调用注解的属性，获取属性值System.out.println(annotation.color());System.out.println(annotation.value());System.out.println(annotation.arrayAttr().length);System.out.println(annotation.lamp().nextLamp().name());//调用注解属性的值System.out.println(annotation.annotationAttr().value());}Method mainMethod = AnnotationTest.class.getMethod("main", String[].class);ItcastAnnotation annotation2 = (ItcastAnnotation)mainMethod.getAnnotation(ItcastAnnotation.class);System.out.println(annotation2.value());}@Deprecated //将方法设置为过时public static void sayHello(){System.out.println("hi,传智播客");}@override //对父类方法重写（覆盖）}import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;import cn.itcast.day1.EnumTest;//元注解，该注解使得自定义的注解的生命周期最长@Retention(RetentionPolicy.RUNTIME)//设置注解在方法和类（接口、枚举...）上使用@Target({ElementType.METHOD,ElementType.TYPE})/***自定义注解*/public @interface ItcastAnnotation {//定义注解的属性，默认属性为blueString color() default "blue";//特殊的属性，使用时可直接赋值String value();//数组类型的属性int[] arrayAttr() default {3,4,4};//枚举类型的属性EnumTest.TrafficLamp lamp() default EnumTest.TrafficLamp.RED;//注解类型的属性MetaAnnotation annotationAttr() default @MetaAnnotation("lhm");}public @interface MetaAnnotation {String value();}

7：泛型的使用

public static void main(String[] args) throws Exception {// TODO Auto-generated method stubArrayList collection1 = new ArrayList();collection1.add(1);collection1.add(1L);collection1.add("abc");//int i = (Integer)collection1.get(1);ArrayList<String> collection2 = new ArrayList<String>();//collection2.add(1);//collection2.add(1L);collection2.add("abc");String element = collection2.get(0);//new String(new StringBuffer("abc"));Constructor<String> constructor1 = String.class.getConstructor(StringBuffer.class);String str2 = constructor1.newInstance(/*"abc"*/new StringBuffer("abc"));System.out.println(str2.charAt(2));//利用泛型通过反射向某一集合中添加不同类型的数据ArrayList<Integer> collection3 = new ArrayList<Integer>();//通过编译后的对象一样System.out.println(collection3.getClass() == collection2.getClass());//true//collection3.add("abc");//添加字符串collection3.getClass().getMethod("add", Object.class).invoke(collection3, "abc");System.out.println(collection3.get(0));//使用？通配符printCollection(collection3);        //通配符的扩展/***限定上边界：*  正确：Vector<? extends Number> = new  Vector<Integer>();*  错误：Vector<? extends Number> = new  Vector<String>();*限定下边界*  正确：Vector<? supter Integer> = new  Vector<Number>();*  错误：Vector<? supter Integer> = new  Vector<Byte>();*///Class<Number> x = String.class.asSubclass(Number.class);Class<?> y;Class<String> x ;//Class.forName("java.lang.String");>>>?表示返回任意类型//泛型Map的使用HashMap<String,Integer> maps = new HashMap<String, Integer>();maps.put("zxx", 28);maps.put("lhm", 35);maps.put("flx", 33);Set<Map.Entry<String,Integer>> entrySet = maps.entrySet();for(Map.Entry<String, Integer> entry : entrySet){System.out.println(entry.getKey() + ":" + entry.getValue());}//返回参数交集类型add(3,5);Number x1 = add(3.5,3);Object x2 = add(3,"abc");//使用自定义的泛型方法swap(new String[]{"abc","xyz","itcast"},1,2);//swap(new int[]{1,3,5,4,5},3,4);//只能是引用类型才可以作为泛型参数Object obj = "abc";String x3 = autoConvert(obj);//（返回）类型参数的类型推断copy1(new Vector<String>(),new String[10]);copy2(new Date[10],new String[10]);//copy1(new Vector<Date>(),new String[10]);//定义泛型变量的运用GenericDao<ReflectPoint> dao = new GenericDao<ReflectPoint>();dao.add(new ReflectPoint(3,3));//String s = dao.findById(1);//Vector<Date> v1 = new Vector<Date>();//通过方法（利用泛型）获取参数类型//利用反射、获取泛型对象参数Method applyMethod = GenericTest.class.getMethod("applyVector", Vector.class);//获取方法Type[] types = applyMethod.getGenericParameterTypes();//获取所有参数ParameterizedType pType = (ParameterizedType)types[0];System.out.println(pType.getRawType());//得到原始类型System.out.println(pType.getActualTypeArguments()[0]);}public static void applyVector(Vector<Date> v1){}//将任意类型的数组填充为统一类型的对象private static <T> void fillArray(T[] a,T obj){for(int i=0;i<a.length;i++){a[i] = obj;}}//自定义泛型方法，自动转换类型private static <T> T autoConvert(Object obj){return (T)obj;}//自定义泛型方法private static <T> void swap(T[] a,int i,int j){T tmp = a[i];a[i] = a[j];a[j] = tmp;}private static <T> T add(T x,T y){return null;}//使用通配符 ？（应用变量） 这样可以传递 多种类型 public static void printCollection(Collection<?> collection){//collection.add(1); //不能调用此的方法（与参数类型有关）//size() 方法与参数类型无关 ，可以使用System.out.println(collection.size());for(Object obj : collection){System.out.println(obj);}}//打印任意类型的集合public static <T> void printCollection2(Collection<T> collection){//collection.add(1);System.out.println(collection.size());for(Object obj : collection){System.out.println(obj);}}//将任意类型的集合拷贝到某一特定的集合public static <T> void copy1(Collection<T> dest,T[] src){}

import java.util.Set;//定义泛型变量的运用（模拟数据库的操作）//dao data access object--->crudpublic class GenericDao<E>  {public void add(E x){}public E findById(int id){return null;}public void delete(E obj){}public void delete(int id){}public void update(E obj){}public static <E> void update2(E obj){}public E findByUserName(String name){return null;}public Set<E> findByConditions(String where){return null;}}