day27--Java集合10 - ToB企服应用市场:ToB评测及商务社交产业平台

package practice.collections_homework;
import java.util.ArrayList;
import java.util.Collections;
@SuppressWarnings("all")
public class HomeWork01 {
public static void main(String[] args) {
ArrayList arrayList = new ArrayList();
arrayList.add(new News("新冠确诊病例超千万，数百万印度信徒赴恒河“圣浴”引民众担忧"));
arrayList.add(new News("男子突然想起两个月前掉的鱼还在网兜里，捞起一看赶紧放生"));
Collections.reverse(arrayList);//倒序遍历法一
//int size = arrayList.size();
//for (int i = size-1; i >=0 ; i--) {//倒序遍历法二
//System.out.println(arrayList.get(i));
//}
for (Object o : arrayList) {
System.out.println(o);
}
}
}
class News {
private String title;//标题
private String content;//内容
public News(String title) {//实例化对象时只初始化标题
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;
}
@Override
public String toString() {//打印对象时只打印标题
if(title==null){
return "";
}
if (title.length() > 15) {
// substring:返回一个字符串，该字符串是此字符串的子字符串。
// 子串开始于指定beginIndex并延伸到字符索引endIndex- 1
String sub = title.substring(0, 15);
return sub + "...";
} else {
return title ;
}
}
}

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package practice.collections_homework;
import java.util.ArrayList;
import java.util.Iterator;
@SuppressWarnings("all")
public class HomeWork02 {
public static void main(String[] args) {
ArrayList arrayList = new ArrayList();
Car car1 = new Car("宝马", 400_000);
Car car2 = new Car("宾利", 5_000_000);
Car car3 = new Car("法拉利", 8_000_000);
//add
arrayList.add(car1);
arrayList.add(car2);
arrayList.add(car3);
//增强for
for (Object o:arrayList) {
System.out.println(o);
}
//remove
arrayList.remove(car3);
System.out.println(arrayList);//[Car{name='宝马', price=400000}, Car{name='宾利', price=5000000}]
//contains
System.out.println(arrayList.contains(car1));//true
//size
System.out.println(arrayList.size());//2
//isEmpty
System.out.println(arrayList.isEmpty());//false
//addAll(Collection<? extends E> c)
ArrayList arrayList2 =new ArrayList();
arrayList2.addAll(arrayList);
Iterator iterator2 = arrayList2.iterator();//迭代器
while (iterator2.hasNext()) {
Object next = iterator2.next();
System.out.println(next);
}
//clear
arrayList.clear();
System.out.println(arrayList);//[]
//containsAlll(Collection<?> c)
System.out.println(arrayList.containsAll(arrayList2));//false
//removeAlll(Collection<?> c)
ArrayList arrayList3 = new ArrayList();
arrayList3.add(car1);
arrayList2.removeAll(arrayList3);
System.out.println(arrayList2);//[Car{name='宾利', price=5000000}]
}
}
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(int price) {
this.price = price;
}
@Override
public String toString() {
return "Car{" +
"name='" + name + '\'' +
", price=" + price +
'}';
}
}

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package practice.collections_homework;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
@SuppressWarnings("all")
public class HomeWork03 {
public static void main(String[] args) {
Map m = new HashMap();
m.put("jack", 650);
m.put("tom", 1200);
m.put("smith", 2900);
m.put("jack", 2600);//将jack的工资更改为2600
System.out.println(m);
//为所有员工工资加薪100
//使用keySet
Set keySet = m.keySet();
for (Object key : keySet) {
m.put(key, (Integer) m.get(key) + 100);
}
System.out.println(m);
//遍历key
for (Object key : keySet) {
System.out.println(key);
}
//遍历value
for (Object key : keySet) {
System.out.println(m.get(key));
}
//使用EntrySet遍历
Set entrySet = m.entrySet();
//增强for
for (Object entry:entrySet) {
System.out.println(((Map.Entry)entry).getKey());
System.out.println(((Map.Entry)entry).getValue());
}
//迭代器
Iterator iterator = entrySet.iterator();
while (iterator.hasNext()) {
Map.Entry next = (Map.Entry) iterator.next();
System.out.println(next.getKey());
System.out.println(next.getValue());
}
}
}

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TreeSet treeSet = new TreeSet();
treeSet.add(new Person());

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