＜二＞ API-filter

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  先看一下源码关于这个API的介绍

  /**
     * Returns a stream consisting of the elements of this stream that match
     * the given predicate.
     * 大致意思就是：将这个流中和给定谓词匹配的元素组成一个流返回
     * <p>This is an <a href="package-summary.html#StreamOps">intermediate
     * operation</a>.
     * 这是一个中间操作
     * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
     *                  <a href="package-summary.html#Statelessness">stateless</a>
     *                  predicate to apply to each element to determine if it
     *                  should be included
     * @return the new stream  返回一个新的流
     */
    Stream<T> filter(Predicate<? super T> predicate);

  通过源码可以看出，filter的作用和名字一样起到了过滤的作用。

  用法如下：

Person p1 = new Person("张", new BigDecimal("2.0"));
Person p2 = new Person("王", new BigDecimal("4.0"));
Person p3 = new Person("李", new BigDecimal("7.0"));
Person p4 = new Person("王", new BigDecimal("5.0"));
Person p5 = new Person("赵", new BigDecimal("5.0"));
List<Person> pList = new ArrayList<>();
pList.add(p1);
pList.add(p2);
pList.add(p4);
pList.add(p3);
pList.add(p5);
System.out.println("未过滤:" + pList);
List<Person> collect = pList.stream().filter(item -> item.getSalary().compareTo(new BigDecimal("5")) >= 0).collect(Collectors.toList());
System.out.println("过滤:" + collect);