Java8学习笔记(三)-Lambda表达式深入与流初步

一、关于jdk8对接口的新定义

        增加了默认的方法

        增加了静态的方法

二、对于lambda表达式，必须要有其上下文，才能推断其类型

package cn.org.kingdom.jdk8;public class Test3 {public static void main(String[] args) {TheInterface i1 = ()->{};System.out.println(i1.getClass().getInterfaces()[0]);TheInterface2 i2 = ()->{};System.out.println(i2.getClass().getInterfaces()[0]);/* *()->{};的类型必须依靠其上下文  */new Thread(()->{System.out.println("执行线程操作");}).start();}}@FunctionalInterfaceinterface TheInterface{public void method();}@FunctionalInterfaceinterface TheInterface2{public void method2();}

三、接下来看一个案例：要求对一个集合里的字符串的小写改为大写

List<String> list = Arrays.asList("hello","world","sky","moon");List<String> list2  = new ArrayList<String>();list.forEach((e)->{//先放入到list2list2.add(e.toUpperCase());});list2.forEach(e->System.out.println(e));

　对于以上代码并没有得到太多的简化，逻辑上与我们之前的代码逻辑差不多，下面我们采用流的方式来编写，首先来观察一下Collection接口中的方法

/**     * Returns a sequential {@code Stream} with this collection as its source.     *     * <p>This method should be overridden when the {@link #spliterator()}     * method cannot return a spliterator that is {@code IMMUTABLE},     * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}     * for details.)     *     * @implSpec     * The default implementation creates a sequential {@code Stream} from the     * collection's {@code Spliterator}.     *     * @return a sequential {@code Stream} over the elements in this collection     * @since 1.8     */    default Stream<E> stream() {        return StreamSupport.stream(spliterator(), false);    }    /**     * Returns a possibly parallel {@code Stream} with this collection as its     * source.  It is allowable for this method to return a sequential stream.     *     * <p>This method should be overridden when the {@link #spliterator()}     * method cannot return a spliterator that is {@code IMMUTABLE},     * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}     * for details.)     *     * @implSpec     * The default implementation creates a parallel {@code Stream} from the     * collection's {@code Spliterator}.     *     * @return a possibly parallel {@code Stream} over the elements in this     * collection     * @since 1.8     */    default Stream<E> parallelStream() {        return StreamSupport.stream(spliterator(), true);    }　

使用stream的方式改写

List<String> list = Arrays.asList("hello", "world", "sky", "moon");list.stream().map(item -> item.toUpperCase()).forEach(item -> System.out.println(item));System.out.println("=================");list.stream().map(String::toUpperCase).forEach(e->System.out.println(e));