java8笔记一

package com;

import java.util.*;
import java.util.function.Predicate;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

/**
* @author nidayu
* @Description: 测试Java8特性
* @date 2015/10/8
*/
public class TestJava8 {

//不包含的集合！
private static Set NON_WORDS = new HashSet<String>(){{add("ni"); add("DA"); add("yu");}};

public Map wordFreq(String words){
TreeMap<String, Integer> wordMap = new TreeMap<String, Integer>();
Matcher m = Pattern.compile("\\w+").matcher(words);
while(m.find()){
String word = m.group().toLowerCase();
if (!NON_WORDS.contains(word)){
if (wordMap.get(word) == null){
wordMap.put(word, 1);
}else{
wordMap.put(word, wordMap.get(word) + 1);
}
}
}
return wordMap;
}

public static void main(String[] args){
//初始化List
List<String> places = Arrays.asList("Buenos Aires", "Córdoba", "La Plata");
places.stream().filter(name -> name.startsWith("C")).forEach(name -> System.out.println(name));

//排序
List<Integer> comList = new ArrayList<>();
comList.add(1);comList.add(0);comList.add(3);comList.add(7);comList.add(6);comList.add(5);
Comparator<Integer> c1 = (x, y) -> x-y;
Comparator<Integer> c2 = c1.reversed();
Comparator<Integer> c3 = (x, y) -> y-x;
System.out.println(
comList.stream()
.min((x, y) -> x - y)
.get()
);
System.out.println("min = " + comList.stream().min(c1).get());
System.out.println("max = " + comList.stream().max(c1).get());
System.out.println("max = " + comList.stream().min(c2).get());
System.out.println("max = " + comList.stream().min(c3).get());

//方法覆盖
new Thread(() -> System.out.println("hello, world")).start();

//过滤循环输出
Predicate<String> p = name -> !name.startsWith("Mr");
List l = new ArrayList<String>();
l.add("Mr Ni");l.add("Ms Zhang");l.add("Ms Lv");l.add("Ms Wang");
l.stream().filter(p).forEach(name -> System.out.println(name));

//找完美数
System.out.println(
IntStream.range(1, 12).filter(t -> 12%t == 0).sum()
);

//过滤拼接
List<String> list = new ArrayList<String>();
list.add("ni");
list.add("da");
list.add("yu");
list.add("ni");
System.out.println(
list.parallelStream() //并发的，和stream()不一样
.filter(name -> name!=null)
.filter(name -> name.length()>1)
.map(name -> name.substring(0, 1).toUpperCase()+name.substring(1, name.length()))
.collect(Collectors.joining(","))
);

//循环遍历
List<String> list1 = new ArrayList<String>();
list.stream().filter(w -> !NON_WORDS.contains(w)).forEach(w -> list1.add(w));
for (int i=0;i<list1.size();i++){
System.out.println(list1.get(i));
}

//统计！
TreeMap<String, Integer> wordMap = new TreeMap<String, Integer>();
list.stream().map(w -> w.toUpperCase())
.filter(w -> !NON_WORDS.contains(w))
.forEach(w -> wordMap.put(w, wordMap.getOrDefault(w, 0) + 1));
for (String key: wordMap.keySet()){
System.out.println(key + " ... "+wordMap.get(key));
}
}
}