函數(shù)式編程

1. 過(guò)濾
   Collections.filter(原內(nèi)容，過(guò)濾規(guī)則)；返回一個(gè)新的list

/**
     * 過(guò)濾，找出回文
     */
    public static void test02() {
        List<String> list = Lists.newArrayList("big", "mom", "hoh", "dad", "refer", "Viking");
        Collection<String> list2 = Collections2.filter(list, new Predicate<String>() {

            // 匿名內(nèi)部類，只使用一次，因?yàn)闆](méi)有對(duì)象名
            public boolean apply(String input) {
                // 這里不滿足要求就會(huì)被過(guò)濾出去
                return new StringBuilder(input).reverse().toString().equals(input);
            }
        });

        for (String temp : list2) {
            System.out.println(temp);
        }
    }

2. 轉(zhuǎn)換
   Collections2.transform();

public static void main(String[] args) {
        //類型轉(zhuǎn)換，function的意思是函數(shù)
        List<Long> longtime=new ArrayList<>();
        longtime.add(100000000L);
        longtime.add(999999999999999L);
        longtime.add(200000000L);
        
        Collection<String> timeStrCol=Collections2.transform(longtime, new Function<Long, String>() {

            public String apply(Long input) {
                
                return new SimpleDateFormat("yyyy-MM-dd").format(input);
            }
        });
        
        for(String temp:timeStrCol){
            System.out.println(temp);
        }
    }

函數(shù)嵌套使用

public static void main(String[] args) {
        //組合式函數(shù)編程
        //確保容器內(nèi)字符串的長(zhǎng)度不超過(guò)5，超過(guò)得部分截?cái)?，然后全轉(zhuǎn)換成大寫。
        List<String> list=Lists.newArrayList("hello","happiness","Viking","iloveu");
        
        Function<String, String> f1=new Function<String, String>() {
            //f1判斷是否長(zhǎng)度是否大于5，并采取截?cái)嗖僮?            public String apply(String input) {
                return input.length()>5?input.substring(0, 5):input;
            }
        };
        
        Function<String, String> f2=new Function<String, String>() {
            //f2將字符串轉(zhuǎn)成大寫的
            public String apply(String input) {
                return input.toUpperCase();
            }
        };
        
        //組合函數(shù)
        Function<String, String> f=Functions.compose(f1, f2);
        
        Collection<String> col=Collections2.transform(list, f);
        
        for(String temp:col){
            System.out.println(temp);
        }
    }

3. 約束
   似乎guava里面沒(méi)有這個(gè)Constraint這個(gè)類或者借口了

集合的操作

• 交集
  sets.intersection();
• 差集
  sets.difference();
• 并集
  sets.union();

public static void main(String[] args) {
        //集合操作
        Set<Integer> set1=Sets.newHashSet(1,2,3,4,5,6);
        Set<Integer> set2=Sets.newHashSet(4,5,6,7,8,9);
        
        Set<Integer> intersectionSet=Sets.intersection(set1, set2);
        System.out.println("交集：");
        for(Integer i:intersectionSet)
            System.out.print(i+"\t");
        
        Set<Integer> differenceSet=Sets.difference(set1, set2);
        System.out.println("\n"+"差集：");
        for(Integer i:differenceSet)
            System.out.print(i+"\t");
        
        Set<Integer> unionSet=Sets.union(set1, set2);
        System.out.println("\n"+"并集：");
        for(Integer i:unionSet)
            System.out.print(i+"\t");
        
    }