Collections.unmodifiableXX函数使用

package cn.vicky;import java.util.Collections;import java.util.HashSet;import java.util.Set;public class MySet {private Set<String> set = new HashSet<String>();public Set<String> getSet(){return set;}public Set<String> getUnSet(){return Collections.unmodifiableSet(set); // 返回的Set无法添加数据。}public static void main(String[] args) {MySet m = new MySet();m.getSet().add("1");m.getSet().add("2");m.getSet().add("3");// 将会出错// m.getUnSet().add("4"); // throw java.lang.UnsupportedOperationException.// 判断类，或接口，是否是指定类的父类，或接口System.out.println(m.getClass().isAssignableFrom(Object.class));System.out.println(m.getClass().isAssignableFrom(MySetChild.class));// 将一个类Object对象，转换为其真实类的父类Object obj = new MySetChild();MySet m2 = MySet.class.cast(obj);System.out.println(m2);// 获得类的子类Class clazz = m2.getClass().asSubclass(MySetChild.class);System.out.println(clazz);}}

false
true
cn.vicky.MySetChild@c17164
class cn.vicky.MySetChild

 

 

 

使用：

 

public class ComponentRegistry{ ComponentRegistry() { componentSet = new LinkedHashSet(); } public Object getComponent(Class type) { Object matchingComponent = null; Iterator i$ = componentSet.iterator(); do { if(!i$.hasNext()) break; Object component = i$.next(); if(type.isAssignableFrom(component.getClass())) { if(matchingComponent != null) throw new MissingResourceException("More than one matching component", type.getName(), null); matchingComponent = component; } } while(true); if(matchingComponent == null) throw new MissingResourceException("No matching components", type.getName(), null); else return type.cast(matchingComponent); } void addComponent(Object component) { componentSet.add(component); } public Iterator iterator() { return Collections.unmodifiableSet(componentSet).iterator(); } private LinkedHashSet componentSet;}