记录JDK 1.8 新特性

package newFeatures8;import java.util.List;import java.util.function.Predicate;import java.util.stream.Collectors;import java.util.Arrays;import java.util.IntSummaryStatistics;public class LambdaExpress {public static void main(String[] args) {//Haha.main(args);// 使用Java 8的方法引用更方便，方法引用由::双冒号操作符标示，// 看起来像C++的作用域解析运算符List<String> features = Arrays.asList("Lambdas", "Default Method", "Stream API", "Date and Time API");features.forEach(System.out::println);//stream():将list集合变成流的形式//map(功能函数):对集合里的元素进行运算、操作//forEach():遍历元素List<Double> costBeforeTax = Arrays.asList(100.08, 200.0, 300.0, 400.0, 500.0);costBeforeTax.stream().map((cost) -> cost + .12*cost).forEach(cost->{System.out.println(String.format("%.2f", cost));});//reduce():返回唯一值：如单个求和double bill = costBeforeTax.stream().map((cost) -> cost + .12*cost).reduce((sum, cost) -> sum + cost).get();System.out.println("Total : " + String.format("%.2f", bill));//filter():过滤器返回stream //collect():通过流返回新的集合// 创建一个字符串列表，每个字符串长度大于2List<String> strList=Arrays.asList("addd","bd","c","dss");List<String> filtered = strList.stream().filter(x -> x.length()> 2).collect(Collectors.toList());System.out.printf("Original List : %s, filtered list : %s %n", strList, filtered);// 将字符串换成大写并用逗号链接起来List<String> G7 = Arrays.asList("USA", "Japan", "France", "Germany", "Italy", "U.K.","Canada");String G7Countries = G7.stream().map(x -> x.toUpperCase()).collect(Collectors.joining(", "));System.out.println(G7Countries);//本例展示了如何利用流的 distinct() 方法来对集合进行去重复。// 用所有不同的数字创建一个正方形列表List<Integer> numbers = Arrays.asList(9, 10, 3, 4, 7, 3, 4);List<Integer> distinct = numbers.stream().map( i -> i*i).distinct().collect(Collectors.toList());System.out.printf("Original List : %s,  Square Without duplicates : %s %n", numbers, distinct);/*IntStream、LongStream 和 DoubleStream 等流的类中，有个非常有用的方法叫做 summaryStatistics() 。可以返回 IntSummaryStatistics、LongSummaryStatistics 或者 DoubleSummaryStatistics，描述流中元素的各种摘要数据。在本例中，我们用这个方法来计算列表的最大值和最小值。它也有 getSum() 和 getAverage() 方法来获得列表的所有元素的总和及平均值。*///获取数字的个数、最小值、最大值、总和以及平均值List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29);IntSummaryStatistics stats = primes.stream().mapToInt((x) -> x).summaryStatistics();//该类设计的巧妙之处就是/*private int min = Integer.MAX_VALUE;把最大值赋给min    private int max = Integer.MIN_VALUE;把最小值赋给max*///IntSummaryStatistics 类默认会执行的方法/* @Override    public void accept(int value) {        ++count;        sum += value;        min = Math.min(min, value);        max = Math.max(max, value);    }*///重写了toString()方法/* public String toString() {        return String.format(            "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}",            this.getClass().getSimpleName(),            getCount(),            getSum(),            getMin(),            getAverage(),            getMax());   }*/System.out.println(stats.toString());System.out.println("Highest prime number in List : " + stats.getMax());System.out.println("Lowest prime number in List : " + stats.getMin());System.out.println("Sum of all prime numbers : " + stats.getSum());System.out.println("Average of all prime numbers : " + stats.getAverage());}}class Haha{public interface BB{//1.8 开始 接口可以有默认的实现方法 default  void  aa(){System.out.println("hah");}//1.8 开始 接口可以有静态的实现方法 static  void  bb(){System.out.println("hah");}}public static void main(String args[]){    List<String> languages = Arrays.asList("Java", "Scala", "C++", "Haskell", "Lisp");     System.out.println("Languages which starts with J :");    filter(languages, (String str)->str.startsWith("J"));         System.out.println("Languages which ends with a ");    filter(languages, (String str)->str.endsWith("a"));     System.out.println("Print all languages :");    filter(languages, (str)->true);     System.out.println("Print no language : ");    filter(languages, (str)->false);     System.out.println("Print language whose length greater than 4:");    filter(languages, (String str)->str.length() > 4);} /*public static void filter(List<String> names, Predicate<String> condition) {    for(String name: names)  {        if(condition.test(name)) {            System.out.println(name + " ");        }    } }*///Predicate:断言类 ：类似于junit//Predicate<String> condition=(String str)->str.length() > 4;// 更好的办法public static void filter(List<String> names, Predicate<String> condition) {    names.stream().filter((name) -> (condition.test(name))).forEach((name) -> {        System.out.println(name + " ");    });   }}

package newFeatures8;import java.util.Arrays;import java.util.List;import java.util.function.Consumer;public class Express {public static void main(String[] args) {List<Double> costBeforeTax = Arrays.asList(100.08, 200.0, 300.0, 400.0, 500.0);/*默认的实现行为如下:     //(s)->System.out.println(s);for (T t : this)         action.accept(t);*/         //在编译器内部 Lambda 表达式被编译成 私有的静态函数  命令行javap -p // private static void lambda$0(java.lang.Double);costBeforeTax.forEach((s)->System.out.println(s));}}