Java8 新特性之集合： removeIf(Predicate<? super E> filter)

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下边是JDK1.8.0_121中接口Collection的部分源码：

/**  * Removes all of the elements of this collection that satisfy the given  * predicate.  Errors or runtime exceptions thrown during iteration or by  * the predicate are relayed to the caller.  *  * @implSpec  * The default implementation traverses all elements of the collection using  * its {@link #iterator}.  Each matching element is removed using  * {@link Iterator#remove()}.  If the collection's iterator does not  * support removal then an {@code UnsupportedOperationException} will be  * thrown on the first matching element.  *  * @param filter a predicate which returns {@code true} for elements to be  *        removed  * @return {@code true} if any elements were removed  * @throws NullPointerException if the specified filter is null  * @throws UnsupportedOperationException if elements cannot be removed  *         from this collection.  Implementations may throw this exception if a  *         matching element cannot be removed or if, in general, removal is not  *         supported.  * @since 1.8  */ default boolean removeIf(Predicate<? super E> filter) {     Objects.requireNonNull(filter);     boolean removed = false;     final Iterator<E> each = iterator();     while (each.hasNext()) {         if (filter.test(each.next())) {             each.remove();             removed = true;         }     }     return removed; }

下边是翻译后的源码（英语渣，如有错误，请指正）：

/**  * 移除集合中满足给定条件的所有元素，错误或者运行时异常发生在迭代时或者把条件传递给调用者的时候。  *  * @implSpec  * 默认的实现贯穿了使用迭代器iterator的集合的所有元素。每一个匹配的元素都将被用Iterator接口中的  * remove()方法移除。如果集合的迭代器不支持移除，则在第一次匹配时就会抛出异常 UnsupportedOperationException  *  * @param filter 令元素移除成功的条件  * @return {@code true} 如果所有的元素都被移除  * @throws NullPointerException 如果有一个过滤器是空的  * @throws UnsupportedOperationException 如果元素不能被从该集合中移除。如果一个匹配元素不能被移除，  *         通常来说，它就不支持移除操作，这时可能抛出这个异常。  * @since 1.8  */ default boolean removeIf(Predicate<? super E> filter) {     Objects.requireNonNull(filter);     boolean removed = false;     final Iterator<E> each = iterator();     while (each.hasNext()) {         if (filter.test(each.next())) {             each.remove();             removed = true;         }     }     return removed; }

下边是实际练习代码

public static void main(String[] args) {    List<Integer> list = new ArrayList<>();    list.add(1);    list.add(2);    list.add(3);    list.add(4);    list.removeIf(s -> s%2==0);               // 过滤掉模2等于0的数    list.forEach(s -> System.out.println(s)); // 输出 1 3    List<String> strings = new ArrayList<>();    strings.add("ab");    strings.add("ac");    strings.add("bc");    strings.add("cd");    Predicate<String> predicate = (s) -> s.startsWith("a"); // 这里单独定义了过滤器    strings.removeIf(predicate);                            // 过滤掉以"a"开头的元素    strings.forEach(s -> System.out.println(s));            // 输出 bc cd}

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