以任何方式设置集合的最大大小? [英] Any way to set max size of a collection?
问题描述
有什么方法可以在Java中设置最大集合大小?
列表< X> list = Arrays.asList(new X [desiredSize]);
//其中X是任何对象类型(包括数组和枚举,
//但不包括原语)
生成的列表是可修改的,但不可调整大小(即 add(e)
和 remove(e)
无效,但set(index,e)$参考:
或者:使用 Guava ,这里是一个静态方法,装饰现有的列表,最大大小
public static< T>列表< T> setMaxSize(
final List< T> input,final int maxSize){
return new ForwardingList< T>(){
@Override
public boolean addAll(Collection< ;? extends T> collection){
return standardAddAll(collection);
}
@Override
public boolean addAll(int index,Collection< ;? extends T> elements){
return standardAddAll(index,elements);
}
public boolean add(T e){
checkMaxSize();
return delegate()。add(e);
}
@Override
public void add(final int index,final T e){
checkMaxSize();
delegate()。add(index,e);
}
private void checkMaxSize(){
if(size()> = maxSize){
throw new UnsupportedOperationException(Maximum Size
+ maxSize +reached);
}
}
@Override
protected List< T> delegate(){
return input;
}
};
}
由于所有标准集合类型都存在ForwardingXxx类,所以您可以自己写类似的装饰器
显然,只有在您的客户端代码使用修饰集合时,这才会有效。如果您更改了底层集合(与Collections.unmodifiableXXX方法一样)。
参考:
is there any way to set maximum size of collection in Java?
You can do this:
List<X> list = Arrays.asList(new X[desiredSize]);
// where X is any Object type (including arrays and enums,
// but excluding primitives)
The resulting list is modifiable, but not resizable (i.e. add(e)
and remove(e)
don't work, but set(index, e)
does).
Reference:
Or: using Guava, here's a static method that decorates an existing List with a maximum size
public static <T> List<T> setMaxSize(
final List<T> input, final int maxSize){
return new ForwardingList<T>(){
@Override
public boolean addAll(Collection<? extends T> collection){
return standardAddAll(collection);
}
@Override
public boolean addAll(int index, Collection<? extends T> elements){
return standardAddAll(index, elements);
}
public boolean add(T e) {
checkMaxSize();
return delegate().add(e);
}
@Override
public void add(final int index, final T e){
checkMaxSize();
delegate().add(index, e);
}
private void checkMaxSize(){
if(size() >= maxSize){
throw new UnsupportedOperationException("Maximum Size "
+ maxSize + " reached");
}
}
@Override
protected List<T> delegate(){
return input;
}
};
}
Since ForwardingXxx classes exist for all standard collection types, you can write yourself similar decorators for other collections as well.
Obviously this will only work if your client code uses the decorated collection. If you change the underlying collection you are screwed (just like the Collections.unmodifiableXXX methods)
Reference:
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