Collection方法接口介紹

Collection接口有3種子類型集合:List、Set和Queue，再下面是一些抽象類，最后是具體實現類，常用的有ArrayList、LinkedList、HashSet、LinkedHashSet、ArrayBlockingQueue等，下面是Collection的所有方法。

這些方法即可以操作Set集合，也可以操作Queue和List集合,下面分別使用Collection集合接口的方法說明

下面是主要方法的演示：  

@Test
????@SuppressWarnings("all")
????public?void?testCollection()?{
????????//?創建Collection接口的實現
????????Collection?collection?=?new?ArrayList<>();
????????//?添加元素
????????collection.add("嘻嘻");
????????String?src?=?"????";
????????collection.add(src);
????????System.out.println(collection);

????????//?創建Collection的實現
????????Collection?coll?=?new?HashSet<>();
????????coll.add("?");
????????coll.add("?");
????????coll.add("?");
????????System.out.println(coll);
????????//?添加一個集合數據
????????collection.addAll(coll);
????????//?輸出集合的長度
????????System.out.println(collection);
????????//?判斷是否包含
????????System.out.println(collection.contains("?"));
????????//?移除元素
????????collection.remove("?");
????????//?添加對象
????????collection.add(new?Person("張三",?23,?5000d));
????????//?當認為兩個對象屬性一致，相等時候，需重寫hashCode?和?equals方法
????????System.out.println(collection.contains(new?Person("張三",?23,?5000d)));

????????System.out.println("-------");
????????collection.add(null);
????
????????Collection?collection1?=?new?ArrayList<>();
????????collection1.add("嘻嘻");
????????collection1.add("?");
????????//?求兩個集合的交集(只保留collection1存在的元素)
????????collection.retainAll(collection1);
????????System.out.println(collection);
????????//?清空元素
????????collection.clear();
????????System.out.println(collection);
????}

java8新特性操作集合

使用lambda表達式遍歷集合

java8為Collection的父接口(Iterable)提供了一個默認的Foreach方法，我們可以使用它進行集合遍歷 

?@Test
????public?void?testForeach()?{
????????Collection?collection?=?new?ArrayList<>();
????????collection.add("i");
????????collection.add("love");
????????collection.add("china");
????????//?foreach遍歷
????????collection.forEach(e->?System.out.println(e));
????????//?可以使用方法引用簡寫
????????collection.forEach(System.out::println);
????????//?或者迭代器的forEachRemaining方法
???????collection.iterator().forEachRemaining(System.out::println);
????}

使用java8的predicate操作集合  

?@Test
????public?void?testPredicate()?{
????????Collection?collection?=?new?ArrayList<>();
????????//?添加0-49
????????for?(int?i?=?0;?i?<?50;?i++)?{
????????????collection.add(i);
????????}

????????//?移除10-49的數字
????????collection.removeIf(e?->?(e?>?9?&&?e?<?50));
????????System.out.println(collection);//?輸出[0,?1,?2,?3,?4,?5,?6,?7,?8,?9]
????}

基于流操作集合

java8之后引入了Stream相關流操作java集合，通過流大大簡化了對集合操作

@Test

????public?void?testIntStream()?{
????????Collection?collection?=?new?ArrayList<>();
????????Random?random?=?new?Random();

????????for?(int?i?=?0;?i?<?10;?i++)?{
????????????collection.add(random.nextInt(100));
????????}
????????System.out.println(collection);
????????//?collection存儲的數值是包裝類型，可以將其轉換為IntStream
????????IntStream?intStream?=?collection.stream().mapToInt(e?->?e);
????????//?intStream.forEach(System.out::println);
????????System.out.println(collection.stream().mapToInt(e?->?e).sum());
????????//?輸出最大值
????????collection.stream().mapToInt(e?->?e).max().ifPresent(System.out::println);
????????//?輸出最小值
????????collection.stream().mapToInt(e?->?e).min().ifPresent(System.out::println);
????????//?統計大于50的數
????????System.out.println(collection.stream().filter(e?->?e?>?50).count());
????????//?原集合每一個值加1
????????collection.stream().mapToInt(e->?e+1).forEach(System.out::println);
????????//?排序
????????collection.stream().mapToInt(e->?e).sorted().forEach(System.out::println);
????????//?原數值每一個元素擴大2倍
????????int[]?ints?=?collection.stream().mapToInt(e?->?e?<<?1).toArray();
????????//?輸出原數組
????????System.out.println(Arrays.toString(ints));
????????//?將數組轉流
????????IntStream?stream?=?Arrays.stream(ints);
????????//?輸出流平均數
????????System.out.println(stream.average().getAsDouble());
????}

以上就是動力節點java培訓機構的小編針對“Java中collection常用方法詳解”的內容進行的回答，希望對大家有所幫助，如有疑問，請在線咨詢，有專業老師隨時為你服務。