Set

Set集合接口也继承了Collection集合接口，此集合的元素是无序的，且不允重复。元素默认为正序排序

API方法实例

size

@Test
public void size() {
    //size: 返回集合数据的长度
    Set<Object> set = new HashSet<>();
    int size = set.size();
    //没有添加数据，打印为0
    System.out.println(size);
    //打印集合为空
    System.out.println(set);
}

isEmpty

@Test
public void isEmpty() {
    //isEmpty:判断集合是否为空，空则返回true，否则false
    Set<Object> set = new HashSet<>();
    boolean empty = set.isEmpty();
    System.out.println(empty);
}

contains

@Test
public void contains() {
    //contains:判断集合是否存在指定的元素
    Set<Object> set = new HashSet<>();
    //不存在这个指定的字符，返回为false
    boolean contains = set.contains("contains");
    System.out.println(contains);
}

iterator

@Test
public void iterator() {
    //iterator:返回一个迭代器接口，用于遍历集合
    Set<Object> set = new HashSet<>();
    set.add("iterator");
    Iterator<Object> iterator = set.iterator();
    //使用迭代器接口方法遍历集合数据
    iterator.forEachRemaining(System.out::print);
}

toArray(无参)

@Test
public void toArray() {
    //toArray无参: 将集合转换为数组
    Set<Object> set = new HashSet<>();
    set.add("toArray");
    Object[] toArray = set.toArray();
    //使用增强for循环遍历集合
    for (Object o : toArray) {
        System.out.println(o);
    }
}

toArray有参

@Test
public void toArrayArgs() {
    //toArray有参: 将集合转换为数组，并用参数作为匹配值
    Set<Object> set = new HashSet<>();
    set.add(1);
    set.add(2);
    set.add(3);
    //利用指定参数匹配集合数据，如果超出集合的长度则超出的值打印为null
    Object[] toArray = set.toArray(new Object[]{1,2,3,4});
    for (Object o : toArray) {
        System.out.println(o);
    }
}

add

@Test
public void add() {
    //add: 往集合里添加一条数据，不可重复
    Set<Object> set = new HashSet<>();
    set.add(2);
    set.add(1);
    //两个重复的值，只会打印一次
    System.out.println(set);
}

remove

@Test
public void remove() {
    //remove: 移除集合指定元素
    Set<Object> set = new HashSet<>();
    set.add("remove");
    //移除集合中添加的字符
    boolean remove = set.remove("remove");
    System.out.println(remove);
}

containsAll

@Test
public void containsAll() {
    //containsAll: 根据Collection集合比较set判断内容
    Set<Object> set = new HashSet<>();
    set.add("containsAll");
    Collection<Object> collection = new HashSet<>();
    //添加匹配set集合的值
    collection.add("containsAll");
    //Collection里的值和set集合的值一直，所以判断为true
    System.out.println(set.containsAll(collection));
}

addAll

@Test
public void addAll() {
    //addAll: 根据Collection集合批量添加数据
    Set<Object> set = new HashSet<>();
    Collection<Object> collection = new HashSet<>();
    collection.add("addAll1");
    collection.add("addAll2");
    //返回为true
    System.out.println(set.addAll(collection));
}

retainAll

@Test
public void retainAll() {
    //retainAll: 根据Collection集合保留指定的值
    Set<Object> set = new HashSet<>();
    set.add("retainAll");
    set.add("retainAll method");
    Collection<Object> collection = new HashSet<>();
    //添加要保留的值
    collection.add("retainAll");
    System.out.println(set.retainAll(collection));
    //此时只打印0号索引值，因为被指定保留
    System.out.println(set);
}

removeAll

@Test
public void removeAll() {
    //removeAll: 根据Collection集合批量移除
    Set<Object> set = new HashSet<>();
    //添加set集合的值
    set.add("remove");
    set.add("removeAll");
    Collection<Object> collection = new HashSet<>();
    //添加要移除的值
    collection.add("remove");
    collection.add("removeAll");
    System.out.println(set.removeAll(collection));
}

clear

@Test
public void clear() {
    //clear: 移除集合所有元素
    Set<Object> set = new HashSet<>();
    set.add("clear");
    set.clear();
    //此时打印集合为空
    System.out.println("set = " + set);
}

equals

@Test
public void equals() {
    //equals: 比较集合对象是否相等
    Set<Object> set1 = new HashSet<>();
    Set<Object> set2 = new HashSet<>();
    //判断两个set集合的对象值是否相等，打印为true
    System.out.println("set1.equals(set2) = " + set1.equals(set2));
}

HashCode

@Test
public void HashCode() {
    //hashCode: 返回哈希值
    Set<Object> set = new HashSet<>();
    set.add("hashCode");
    //随机返回一个整数值
    System.out.println("set.hashCode() = " + set.hashCode());
}

spliterator

@Test
public void spliterator() {
    Set<Object> set = new HashSet<>();
    set.add("spliterator");
    Spliterator<Object> spliterator = set.spliterator();
    //使用Spliterator接口方法遍历集合数据
    spliterator.forEachRemaining(System.out :: println);
}

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