30天学会JAVA—练习题(2021韩顺平)——Day15

集合练习题

public class A01 {
   
	@SuppressWarnings("all")
	public static void main(String[] args) {
   
		ArrayList arrayList = new ArrayList();
		arrayList.add(new Newspaper("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 Newspaper("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"));
		
		//倒序遍历
		for(int i = arrayList.size()-1; i >= 0; i--){
   
			//向下转型
			Newspaper newspaper = (Newspaper) arrayList.get(i);
			System.out.println( processTitle(newspaper.getTitle()));
		}		
}
	//处理新闻标题
	public static String processTitle(String title){
   
		if(title == null){
   
			return "";
		}
		if(title.length() > 15){
   
			return title.substring(0, 15) + "...";
		}else{
   
			return title;
		}				
	}
}
class Newspaper{
   
	private String title;
	private String content;
	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;
	}
	public Newspaper(String title) {
   
		super();
		this.title = title;
	}
	@Override
	public String toString() {
   
		return "\n"+"Newspaper [title=" + title + "]";
	}		
}

public class A02 {
   
	@SuppressWarnings("all")
	public static void main(String[] args) {
   
		ArrayList arrayList = new ArrayList();
		//添加
		arrayList.add(new Car("宝马", 400000));
		arrayList.add(new Car("宾利", 5000000));
		System.out.println("原始集合："+arrayList);
		//删除宝马
		arrayList.remove(0);
		System.out.println("删除宝马后："+arrayList);
		System.out.println("查找宾利："+arrayList.contains("宾利"));
		System.out.println("获取元素个数："+arrayList.size());
		System.out.println("判断是否为空："+arrayList.isEmpty());
		//判断是否为空
		
		//清空
// arrayList.clear();
// System.out.println(arrayList);
		
		System.out.println("添加多个元素"+arrayList.addAll(arrayList));
		//查找多个元素是否存在
		//增强for循环遍历
		for(Object obj:arrayList){
   
			System.out.println(obj);
		}
		//迭代器遍历
		Iterator iterator = arrayList.iterator();
		while(iterator.hasNext()){
   
			System.out.println(iterator.next());
		}
	}
}

class Car{
   
	private String name;
	private int price;
	public String getName() {
   
		return name;
	}
	public void setName(String name) {
   
		this.name = name;
	}
	public int getPrice() {
   
		return price;
	}
	public void setPrice(int price) {
   
		this.price = price;
	}
	public Car(String name, int price) {
   
		super();
		this.name = name;
		this.price = price;
	}
	@Override
	public String toString() {
   
		return "\n"+"Car [name=" + name + ", price=" + price + "]";
	}	
}

public class A03 {
   
	@SuppressWarnings("all")
	public static void main(String[] args) {
   
		Map hashMap = new HashMap();
		hashMap.put("jack", 650);
		hashMap.put("tom", 1200);
		hashMap.put("smith", 2900);
		System.out.println(hashMap);
		hashMap.replace("jack", 650,  2600);
		System.out.println(hashMap);
		
		//遍历【 keySet】：为所有员工加薪100元
		Set keySet = hashMap.keySet();
		for(Object obj : keySet){
   
			hashMap.put(obj, (Integer)hashMap.get(obj)+100);
		}
		System.out.println(hashMap);

		//entrySet + 迭代器
		Set entrySet = hashMap.entrySet();
		Iterator iterator = entrySet.iterator();
		while(iterator.hasNext()){
   
			Map.Entry next = (Entry) iterator.next();
			System.out.println(next.getKey() + "-" + next.getValue());
		}
		
		Collection values = hashMap.values();
		for(Object value : values){
   
			System.out.println(value);
		}
	}
}

额……