java的collections集合
时间:2007-05-28 yycnet.yeah.net yyc译
下面这张表格（表一）总结了用一个集合能做的所有事情（亦可对Set和List做同样的事情，尽管List还提供了一些额外的功能）。Map不是从Collection继承的，所以要单独对待。boolean add(Object) ＊保证集合内包含了自变量。如果它没有添加自变量，就返回false（假）boolean addAll(Collection) ＊添加自变量内的所有元素。如果没有添加元素，则返回true（真）void clear() ＊删除集合内的所有元素boolean contains(Object) 若集合包含自变量，就返回“真”boolean containsAll(Collection) 若集合包含了自变量内的所有元素，就返回“真”boolean isEmpty() 若集合内没有元素，就返回“真”Iterator iterator() 返回一个反复器，以用它遍历集合的各元素boolean remove(Object) ＊如自变量在集合里，就删除那个元素的一个实例。如果已进行了删除，就返回“真”boolean removeAll(Collection) ＊删除自变量里的所有元素。如果已进行了任何删除，就返回“真”boolean retainAll(Collection) ＊只保留包含在一个自变量里的元素（一个理论的“交集”）。如果已进行了任何改变，就返回“真”int size() 返回集合内的元素数量Object[] toArray() 返回包含了集合内所有元素的一个数组
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Boolean add(Object)
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*Ensures that the Collection contains the argument. Returns false if it doesn’t add the argument.
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Boolean addAll(Collection)
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*Adds all the elements in the argument. Returns true if any elements were added.
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void clear()
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*Removes all the elements in the Collection.
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Boolean contains(Object)
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True if the Collection contains the argument.
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Boolean containsAll(Collection)
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True if the Collection contains all the elements in the argument.
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Boolean isEmpty()
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True if the Collection has no elements.
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Iterator iterator()
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Returns an Iterator that you can use to move through the elements in the Collection.
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Boolean remove(Object)
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*If the argument is in the Collection, one instance of that element is removed. Returns true if a removal occurred.
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Boolean removeAll(Collection)
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*Removes all the elements that are contained in the argument. Returns true if any removals occurred.
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Boolean retainAll(Collection)
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*Retains only elements that are contained in the argument (an “intersection” from set theory). Returns true if any changes occurred.
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int size()
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Returns the number of elements in the Collection.
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Object[] toArray()
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Returns an array containing all the elements in the Collection.
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Object[] toArray(Object[] a)
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Returns an array containing all the elements in the Collection, whose type is that of the array a rather than plain Object (you must cast the array to the right type).
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*This is an “optional” method, which means it might not be implemented by a particular Collection. If not, that method throws an UnsupportedOperationException. Exceptions will be covered in Chapter 9.
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