Java容器-引入Guava類庫

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一、目錄

1、唯讀設定

2、函數式編程+組合式編程

3、約束條件

4、集合操作(並集、差集、交集)

二、代碼實現

1、唯讀設定

public static void main(String [] args){        //唯讀設定        List ls=new ArrayList();        ls.add("a");        ls.add("b");        ls.add("c");        //不使用guava的類庫        List <String > readList= Collections.unmodifiableList(ls);        //readList.add("d"); 報錯        //使用guava的類庫        List<String> imutableList= ImmutableList.of("a","b","c");        //imutableList.add("a"); 運行報錯
}

2、函數式編程

（1）函數一：找出集合眾的迴文字串，迴文又稱 mirror word ,backword，是指字串從前面或者後面讀都是一樣的，比如moom 

//結果：moom   因為moon逆序以後還是moom    public static void main(String[] args) {        List<String> list = Lists.newArrayList("dog", "cat", "pig", "moom");        Collection<String> pList=Collections2.filter(list, new Predicate<String>() {            public boolean apply(String s) {                return new StringBuilder(s).reverse().toString().equals(s);            }        });        // 匿名內部類，同時建立對象,Collections2.filter類似過濾器        for(Object o:pList){            System.out.println(o);        }    }

（2）函數二：日期轉換

//結果:1970-01-01    1970-01-24   1970-01-02

 public static void main(String [] args){        Set<Long> timeSet= Sets.newHashSet();        timeSet.add(1000L);        timeSet.add(2000L*1000000);        timeSet.add(3000L*20000);                Collection<String> transList= Collections2.transform(timeSet, new Function<Long, String>() {            public String apply(Long input) {                return new SimpleDateFormat("yyyy-MM-dd").format(input);            }        });        for(String s:transList){            System.out.println(s);        }    }

(3)函數三：組合式編程

public static void main(String [] args){        List<String> list = Lists.newArrayList("happy", "sad", "wahaha");        //方法一        Function<String,String>f1=new Function<String, String>() {            public String apply(String s) {                return s.length()>5&&s.length()<20?s:"error";            }        };        //方法二：字母全部大寫        Function<String, String> f2 = new Function<String, String>() {            public String apply(String input) {                return input.toUpperCase();            }        };        //組合方法        Function<String, String> f = Functions.compose(f1, f2);        Collection resultCol=Collections2.transform(list,f);        for(Object s:resultCol){            System.out.println(s);        }    }

 3、約束條件

 public static void main(String[] args) {        Set<String> sets = Sets.newHashSet();        // 建立約束        Constraint<String> constraint = new Constraint<String>() {            @Override            public String checkElement(String element) {                // 非空驗證                Preconditions.checkNotNull(element);                // 長度限制 5-20,否則報錯                Preconditions.checkArgument(                        element.length() >= 5 && element.length() <= 20,                        element);                return element;            }        };        Set<String> cs = Constraints.constrainedSet(sets, constraint);        // cs.add(null); 報錯java.lang.NullPointerException        //cs.add("qaz"); 報錯java.lang.IllegalArgumentException: qaz    }

 4、交集、並集、差集

 public static void main(String [] args){        Set<Integer> sets=Sets.newHashSet(1,2,3,4,5,6);        Set<Integer> set2=Sets.newHashSet(3,4,5,6,7,8,9);        Sets.SetView<Integer> intersection =Sets.intersection(sets, set2);        for(Integer in:intersection){            System.out.print(in+"  ");        }        System.out.println("");        //差集        Sets.SetView<Integer> intersection2=Sets.difference(sets,set2);        for(Integer in:intersection2){            System.out.print(in+"  ");        }        System.out.println("");        //並集        Sets.SetView<Integer> intersection3=Sets.union(sets,set2);        for(Integer in:intersection3){            System.out.print(in+"  ");        }    }

 

Java容器-引入Guava類庫