关于Collections的描述上一篇文章已经说过，这里我们主要来看一下Collections的实现以及他所提供的静态方法。
//使用private修饰构造函数，确保单例模式
private Collections() {
}
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集合排序、二分查找、列表逆置
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List初始化，复制，求极值
图片.png
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获取线程安全集合：
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我说一下大概的实现原理，以List为例，首先判断List是否实现Randomaccess接口（主要目的是使算法能够在随机和顺序访问的list中表现的更加高效。），关于这个接口可自行百度，不是这里的重点，然后生成相应的SynchronizedList或者SynchronizedRandomAccessList（两者只是算法实现不同，实现原理是一样的），我们看一下源码：
static class SynchronizedList<E>
extends SynchronizedCollection<E>
implements List<E> {
private static final long serialVersionUID = -7754090372962971524L;
final List<E> list;
SynchronizedList(List<E> list) {
super(list);
this.list = list;
}
SynchronizedList(List<E> list, Object mutex) {
super(list, mutex);
this.list = list;
}
public boolean equals(Object o) {
if (this == o)
return true;
synchronized (mutex) {return list.equals(o);}
}
public int hashCode() {
synchronized (mutex) {return list.hashCode();}
}
public E get(int index) {
synchronized (mutex) {return list.get(index);}
}
public E set(int index, E element) {
synchronized (mutex) {return list.set(index, element);}
}
public void add(int index, E element) {
synchronized (mutex) {list.add(index, element);}
}
public E remove(int index) {
synchronized (mutex) {return list.remove(index);}
}
public int indexOf(Object o) {
synchronized (mutex) {return list.indexOf(o);}
}
public int lastIndexOf(Object o) {
synchronized (mutex) {return list.lastIndexOf(o);}
}
public boolean addAll(int index, Collection<? extends E> c) {
synchronized (mutex) {return list.addAll(index, c);}
}
public ListIterator<E> listIterator() {
return list.listIterator(); // Must be manually synched by user
}
public ListIterator<E> listIterator(int index) {
return list.listIterator(index); // Must be manually synched by user
}
public List<E> subList(int fromIndex, int toIndex) {
synchronized (mutex) {
return new SynchronizedList<>(list.subList(fromIndex, toIndex),
mutex);
}
}
@Override
public void replaceAll(UnaryOperator<E> operator) {
synchronized (mutex) {list.replaceAll(operator);}
}
@Override
public void sort(Comparator<? super E> c) {
synchronized (mutex) {list.sort(c);}
}
private Object readResolve() {
return (list instanceof RandomAccess
? new SynchronizedRandomAccessList<>(list)
: this);
}
}
实际上你会发现，SynchronizedList的实现只是内部维护了我们传入的list集合对象，然后对大部分方法用synchronized进行修饰，锁可以根据需要自己定义或者使用list本身，没有什么高深的原理
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返回视图
图片.png
视图我们知道是不可修改的，只能进行查询操作
下面我们来看一下是如何实现生成视图的操作的：以List为例
static class UnmodifiableList<E> extends UnmodifiableCollection<E>
implements List<E> {
private static final long serialVersionUID = -283967356065247728L;
final List<? extends E> list;
UnmodifiableList(List<? extends E> list) {
super(list);
this.list = list;
}
public boolean equals(Object o) {return o == this || list.equals(o);}
public int hashCode() {return list.hashCode();}
public E get(int index) {return list.get(index);}
public E set(int index, E element) {
throw new UnsupportedOperationException();
}
public void add(int index, E element) {
throw new UnsupportedOperationException();
}
public E remove(int index) {
throw new UnsupportedOperationException();
}
public int indexOf(Object o) {return list.indexOf(o);}
public int lastIndexOf(Object o) {return list.lastIndexOf(o);}
public boolean addAll(int index, Collection<? extends E> c) {
throw new UnsupportedOperationException();
}
@Override
public void replaceAll(UnaryOperator<E> operator) {
throw new UnsupportedOperationException();
}
@Override
public void sort(Comparator<? super E> c) {
throw new UnsupportedOperationException();
}
public ListIterator<E> listIterator() {return listIterator(0);}
public ListIterator<E> listIterator(final int index) {
return new ListIterator<E>() {
private final ListIterator<? extends E> i
= list.listIterator(index);
public boolean hasNext() {return i.hasNext();}
public E next() {return i.next();}
public boolean hasPrevious() {return i.hasPrevious();}
public E previous() {return i.previous();}
public int nextIndex() {return i.nextIndex();}
public int previousIndex() {return i.previousIndex();}
public void remove() {
throw new UnsupportedOperationException();
}
public void set(E e) {
throw new UnsupportedOperationException();
}
public void add(E e) {
throw new UnsupportedOperationException();
}
@Override
public void forEachRemaining(Consumer<? super E> action) {
i.forEachRemaining(action);
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
return new UnmodifiableList<>(list.subList(fromIndex, toIndex));
}
\
private Object readResolve() {
return (list instanceof RandomAccess
? new UnmodifiableRandomAccessList<>(list)
: this);
}
}
同样进行上面的一个是否实现RandomAccess接口的操作，不在赘述，直接看UnmodifiableList的源码，同样的内部维护了我们传入的list集合对象，对所有update操作抛出异常，同样无法获取ListIterator，就无法进行修改操作
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