Java集合框架设计模式面试题
迭代器模式
Q1: 集合框架中的迭代器模式是如何实现的？
public class IteratorPatternExample {
public void basicIteratorUsage() {
List<String> list = new ArrayList<>();
list.add("A");
list.add("B");
list.add("C");
Iterator<String> iterator = list.iterator();
while (iterator.hasNext()) {
String element = iterator.next();
System.out.println(element);
}
}
public static class CustomCollection<T> implements Iterable<T> {
private List<T> items = new ArrayList<>();
public void add(T item) {
items.add(item);
}
@Override
public Iterator<T> iterator() {
return new CustomIterator<>(items);
}
private static class CustomIterator<T> implements Iterator<T> {
private List<T> items;
private int position = 0;
public CustomIterator(List<T> items) {
this.items = items;
}
@Override
public boolean hasNext() {
return position < items.size();
}
@Override
public T next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
return items.get(position++);
}
@Override
public void remove() {
if (position <= 0) {
throw new IllegalStateException();
}
items.remove(--position);
}
}
}
}
组合模式
Q2: 集合框架如何使用组合模式？
public class CompositePatternExample {
public interface Component {
void operation();
}
public class Leaf implements Component {
private String name;
public Leaf(String name) {
this.name = name;
}
@Override
public void operation() {
System.out.println("Leaf " + name + " operation");
}
}
public class Composite implements Component {
private List<Component> children = new ArrayList<>();
public void add(Component component) {
children.add(component);
}
public void remove(Component component) {
children.remove(component);
}
@Override
public void operation() {
for (Component component : children) {
component.operation();
}
}
}
public void demonstrateComposite() {
Composite root = new Composite();
Composite branch1 = new Composite();
Composite branch2 = new Composite();
root.add(branch1);
root.add(branch2);
branch1.add(new Leaf("A"));
branch1.add(new Leaf("B"));
branch2.add(new Leaf("C"));
root.operation();
}
}
适配器模式
Q3: 集合框架中的适配器模式体现在哪里？
public class AdapterPatternExample {
public void arrayListAdapter() {
String[] array = {"A", "B", "C"};
List<String> list = Arrays.asList(array);
try {
list.add("D");
} catch (UnsupportedOperationException e) {
System.out.println("不支持修改操作");
}
}
public class SetToListAdapter<E> extends AbstractList<E> {
private Set<E> set;
public SetToListAdapter(Set<E> set) {
this.set = set;
}
@Override
public E get(int index) {
if (index >= set.size()) {
throw new IndexOutOfBoundsException();
}
Iterator<E> iterator = set.iterator();
for (int i = 0; i < index; i++) {
iterator.next();
}
return iterator.next();
}
@Override
public int size() {
return set.size();
}
}
}
装饰器模式
Q4: 集合框架如何使用装饰器模式？
public class DecoratorPatternExample {
public void unmodifiableDecorator() {
List<String> list = new ArrayList<>();
list.add("A");
list.add("B");
List<String> unmodifiableList =
Collections.unmodifiableList(list);
try {
unmodifiableList.add("C");
} catch (UnsupportedOperationException e) {
System.out.println("不能修改不可变列表");
}
}
public class LoggingList<E> extends AbstractList<E> {
private List<E> list;
public LoggingList(List<E> list) {
this.list = list;
}
@Override
public E get(int index) {
System.out.println("Getting element at index: " + index);
return list.get(index);
}
@Override
public void add(int index, E element) {
System.out.println("Adding element at index: " + index);
list.add(index, element);
}
@Override
public E remove(int index) {
System.out.println("Removing element at index: " + index);
return list.remove(index);
}
@Override
public int size() {
return list.size();
}
}
}
工厂模式
Q5: 集合框架中的工厂模式是如何体现的？
public class FactoryPatternExample {
public static class CollectionFactory {
public static <T> List<T> createList(boolean synchronized_) {
return synchronized_ ?
Collections.synchronizedList(new ArrayList<>()) :
new ArrayList<>();
}
public static <T> Set<T> createSet(boolean sorted) {
return sorted ? new TreeSet<>() : new HashSet<>();
}
public static <K, V> Map<K, V> createMap(
boolean synchronized_, boolean sorted) {
if (synchronized_) {
return sorted ?
Collections.synchronizedMap(new TreeMap<>()) :
Collections.synchronizedMap(new HashMap<>());
} else {
return sorted ? new TreeMap<>() : new HashMap<>();
}
}
}
public void demonstrateFactory() {
List<String> syncList =
CollectionFactory.createList(true);
Set<Integer> sortedSet =
CollectionFactory.createSet(true);
Map<String, Integer> syncSortedMap =
CollectionFactory.createMap(true, true);
}
}
Q6: 如何在实际项目中应用这些设计模式？
public class DesignPatternApplicationExample {
public class CompositeIterator<E> implements Iterator<E> {
private Stack<Iterator<E>> stack = new Stack<>();
public CompositeIterator(Iterator<E> iterator) {
stack.push(iterator);
}
@Override
public boolean hasNext() {
if (stack.empty()) {
return false;
}
Iterator<E> iterator = stack.peek();
if (!iterator.hasNext()) {
stack.pop();
return hasNext();
}
return true;
}
@Override
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
Iterator<E> iterator = stack.peek();
E item = iterator.next();
if (item instanceof Iterable) {
stack.push(((Iterable<E>) item).iterator());
}
return item;
}
}
public class ThreadSafeListAdapter<E>
extends AbstractList<E> {
private final List<E> list;
private final Object lock = new Object();
public ThreadSafeListAdapter(List<E> list) {
this.list = list;
}
@Override
public E get(int index) {
synchronized (lock) {
return list.get(index);
}
}
@Override
public void add(int index, E element) {
synchronized (lock) {
list.add(index, element);
}
}
@Override
public E remove(int index) {
synchronized (lock) {
return list.remove(index);
}
}
@Override
public int size() {
synchronized (lock) {
return list.size();
}
}
}
}
面试关键点
- 理解集合框架中的设计模式应用
- 掌握迭代器模式的实现
- 了解组合模式的使用场景
- 熟悉适配器模式的应用
- 掌握装饰器模式的实现
- 理解工厂模式的作用
- 能够组合使用多种设计模式
- 注意设计模式的性能影响
