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……
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