Java8 新特性之集合： removeIf(Predicate

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(Predicatesuper E> filter) {
     Objects.requireNonNull(filter);
     boolean removed = false;
     final Iterator 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(Predicatesuper E> filter) {
     Objects.requireNonNull(filter);
     boolean removed = false;
     final Iterator 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 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 strings = new ArrayList<>();
    strings.add("ab");
    strings.add("ac");
    strings.add("bc");
    strings.add("cd");
    Predicate 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
}