2.2.2.Collection接口

Collection父接口

• 特点: 代表一组任意类型的对象,无序、无下标、不能重复
• 方法
  • boolean add(Object obj) // 添加一个对象
  • boolean addAll(Collection c) // 将一个集合中的所有对象添加到此结合中
  • void clear() // 清空此集合中的所有对象
  • boolean contains(Object o) //检查此集合中是否包含o对象
  • boolean equals(Object o) // 比较此集合是否与指定对象相等
  • boolean isEmpty() // 判断此集合是否为空
  • boolean remove(Object o) // 在此集合中移除o对象
  • int size() // 返回此集合中的元素个数
  • Object[] toArray() // 将此集合转换成数组

public class demo {
    public static void main(String[] args) {
        // 创建集合
        Collection collection = new ArrayList();
        // 添加元素
        collection.add("西瓜");
        collection.add("苹果");
        collection.add("榴莲");
        System.out.println(collection.size());
        System.out.println(collection);
        // 删除元素
        collection.remove("榴莲");
        //collection.clear();
        System.out.println("删除之后:" + collection.size());
        // 遍历元素
        //// 增强for
        for (Object object: collection) {
            System.out.println(object);
        }
        // 使用迭代器
        Iterator it = collection.iterator();
        while (it.hasNext()) {
            String s = (String)it.next();
            System.out.println(s);
            // 不能使用collection的删除方法
            // collection.remove(s)
            it.remove();
        }
        System.out.println("元素个数:" + collection.size());
        // 判断
        System.out.println(collection.contains("西瓜"));
        System.out.println(collection.isEmpty());

        // 2
        class Student {
            private String name;
            private int age;
            public Student(String name, int age) {
                this.name = name;
                this.age = age;
            }

            @Override
            public String toString() {
                return "Student{" +
                        "name='" + name + '\'' +
                        ", age=" + age +
                        '}';
            }
        }
        // 创建collection对象
        Collection collection1 = new ArrayList();
        Student s1 = new Student("张三", 10);
        Student s2 = new Student("李四", 11);
        Student s3 = new Student("王五", 12);
        // 添加数据
        collection1.add(s1);
        collection1.add(s2);
        collection1.add(s3);
        System.out.println("元素个数:" + collection1.size());
        System.out.println(collection1.toString());
        // 删除
        collection1.remove(s1);
        collection1.remove(new Student("王五", 12));
//        collection1.clear();
        System.out.println("删除之后:"+collection1.size());
        // 遍历
        for (Object object: collection1) {
            Student s = (Student) object;
            System.out.println(s.toString());
        }
        Iterator it1 = collection1.iterator();
        while (it1.hasNext()) {
            Student s = (Student)it1.next();
            System.out.println(s.toString());
        }
        // 判断
        System.out.println(collection1.contains(s1));
        System.out.println(collection1.contains(s2));
    }
}