集合 练习1

按要求实现:(1)封装一个新闻类，包含标题和内容属性，提供get、set方法，重写toString方法,打印对象时只打印标题;(2)只提供一个带参数的构造器，实例化对象时，只初始化标题;并且实例化两个对象:新闻一:新冠确诊病例超千万，数百万印度教信徒赴恒河“圣浴”引民众担忧新闻二:男子突然想起2个月前钓的鱼还在网兜里，捞起一看赶紧放生(3)将新闻对象添加到ArrayList集合中，并且进行倒序遍历;(4)在遍历集合过程中，对新闻标题进行处理，超过15字的只保留前15个，然后在后边加“…"(5)在控制台打印遍历出经过处理的新闻标题;

public class Homework01 {public static void main(String[] args) {ArrayList<Object> arrayList = new ArrayList<>();arrayList.add(new News("新冠确诊病例超千万，数百万印度教信徒赴恒河\\"圣浴\\"引民众担忧"));arrayList.add(new News("男子突然想起2个月前钓的鱼还在网兜里，捞起一看赶紧放生"));Collections.reverse(arrayList); //将集合倒序for (int i = 0; i < arrayList.size(); i++) {News news = (News) arrayList.get(i);System.out.println(processTitle(news.getTitle()));}}public static String processTitle(String title){if (title == null) return "";if (title.length()>15) {return title.substring(0,15)+"..."; //截取字符串，范围：[0,15)}else return title;}
}
class News{private String title;private String content;public News(String title) {this.title = title;}public String getTitle() {return title;}public void setTitle(String title) {this.title = title;}public String getContent() {return content;}public void setContent(String content) {this.content = content;}@Overridepublic String toString() {return "News{" +"title='" + title + '\\'' +'}';}
}

输出：

男子突然想起2个月前钓的鱼还在...
新冠确诊病例超千万，数百万印度...

使用ArrayList完成对对象Car {name, price}的各种操作

1.add:添加单个元素
2.remove:删除指定元素
3.contains:查找元素是否存在
4.size:获取元素个数
5.isEmpty:判断是否为空
6.clear:清空
7.addAll:添加多个元素
8.containsAll:查找多个元素是否都存在9.removeAll:删除多个元素
使用增强for和迭代器来遍历所有的car，需要重写Car的toString方法

public class Homework02 {public static void main(String[] args) {ArrayList<Object> arrayList = new ArrayList<>();Car car = new Car("宝马",400000);Car car1 = new Car("宾利",3000000);arrayList.add(car); //添加arrayList.add(car1); //添加System.out.println(arrayList); //[Car{name='宝马', price=400000.0}, Car{name='宾利', price=3000000.0}]arrayList.remove(car); //删除System.out.println(arrayList); //[Car{name='宾利', price=3000000.0}]System.out.println(arrayList.contains(car)); //falseSystem.out.println(arrayList.size()); //1System.out.println(arrayList.isEmpty()); //falsearrayList.addAll(arrayList);System.out.println(arrayList); //[Car{name='宾利', price=3000000.0}, Car{name='宾利', price=3000000.0}]System.out.println(arrayList.containsAll(arrayList)); //trueSystem.out.println("-----------增强for-------------");for (Object o :arrayList) {System.out.println(o);}System.out.println("-----------迭代器-------------");Iterator<Object> iterator = arrayList.iterator();while (iterator.hasNext()) {Object next =  iterator.next();System.out.println(next);}}
}
class Car{private String name;private double price;public Car(String name, double price) {this.name = name;this.price = price;}public String getName() {return name;}public void setName(String name) {this.name = name;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}@Overridepublic String toString() {return "Car{" +"name='" + name + '\\'' +", price=" + price +'}';}
}

输出：

[Car{name='宝马', price=400000.0}, Car{name='宾利', price=3000000.0}]
[Car{name='宾利', price=3000000.0}]
false
1
false
[Car{name='宾利', price=3000000.0}, Car{name='宾利', price=3000000.0}]
true
-----------增强for-------------
Car{name='宾利', price=3000000.0}
Car{name='宾利', price=3000000.0}
-----------迭代器-------------
Car{name='宾利', price=3000000.0}
Car{name='宾利', price=3000000.0}