1.
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLrN2bsJEZlR3YhJHdu92Qvw1cy9GdhNWak5WSn5WaulGb0V3TvwVbvNmLzd2bsJmbj5ycldWYtl2Lc9CX6MHc0RHaiojIsJye.gif)
/**
* 使用Collection接口,增删改查
* ArrayList内部使用数组实现,变相的实现可变长度的数组,ArrayList能够取代数组。
* @author Administrator
*
*/
public class DemoCollection {
public static void main(String[] args) {
Collection c = new ArrayList();
//1.add方法添加数据
c.add(1);//存的是Integer对象
c.add("a");
c.add(new Person(1,"fyt"));
//2.foreach循环对集合进行遍历
for (Object object : c) {
System.out.println(object);
if(object instanceof Person)
{
Person p = (Person)object;
String name = p.getName();
System.out.println(name);
}
}
//3.size方法获取集合大小。
int size = c.size();
//3.contains方法比较集合中是否有某个对象
boolean isContains = c.contains(new Person(1,"fyt"));
System.out.println(isContains);
//4.clear方法,清除集合中数据
// c.clear();
//5.isEmpty方法,判断集合是否为空
boolean isEmpty = c.isEmpty();
//6.迭代器对象对集合进行遍历
Iterator it = c.iterator();
while(it.hasNext())//判断游标右侧是否有数据
{
Object obj = it.next();//返回游标右侧,并移动
if(obj.equals("a"))
it.remove();
System.out.println("游标:"+obj);
}
//6.把c2集合中的数据全部添加到c集合中。
Collection c2 = new ArrayList();
c2.add("b");
c2.add(1);
c.addAll(c2);
System.out.println("c的大小:"+c.size());
for (Object object : c) {
System.out.println(object);
}
//7.把指定的数据从集合中删掉,删除操作量比较大,频繁的移动数据。
boolean isRemove = c.remove(1);
System.out.println(" 删除后c的大小:"+c.size());
//8.集合转数组
Object[] objs = c.toArray();
}
}
View Code
2.
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLrN2bsJEZlR3YhJHdu92Qvw1cy9GdhNWak5WSn5WaulGb0V3TvwVbvNmLzd2bsJmbj5ycldWYtl2Lc9CX6MHc0RHaiojIsJye.gif)
/**
* 引入泛型的概念,规范集合中存储的数据类型。
* @author Administrator
*
*/
public class DemoCollection2 {
public static void main(String[] args) {
//<String> 说明集合中只能存储String字符串
Collection<String> c = new ArrayList<String>();
c.add("a");
c.add("sdb");
for (String str : c) {
System.out.println(str);
}
Collection<Person> c2 = new ArrayList<Person>();
c2.add(new Person(1,"aaa"));
c2.add(new Person(2,"bbbb"));
for (Person p : c2) {
System.out.println(p.getId()+"--"+p.getName());
}
}
}
3.
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLrN2bsJEZlR3YhJHdu92Qvw1cy9GdhNWak5WSn5WaulGb0V3TvwVbvNmLzd2bsJmbj5ycldWYtl2Lc9CX6MHc0RHaiojIsJye.gif)
public class DemoCopy {
public static void main(String[] args) {
List<String> list = new ArrayList<String>();
list.add("z");
list.add("a");
list.add("c");
list.add("b");
List<String> newList= new ArrayList<String>();
newList.add("as");
newList.add("as");
newList.add("as");
newList.add("as");
newList.add("as");
newList.add("as");
//要求新集合的长度必须大于等于原集合
Collections.copy(newList, list);
for (String string : newList) {
System.out.println(string);
}
}
}
4.
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLrN2bsJEZlR3YhJHdu92Qvw1cy9GdhNWak5WSn5WaulGb0V3TvwVbvNmLzd2bsJmbj5ycldWYtl2Lc9CX6MHc0RHaiojIsJye.gif)
/**
* Collections.sort(List list)要求list集合中对象时可排序
* Collections.sort(List list,Comparator comparator) 自定义排序器对象
* @author Administrator
*
*/
public class DemoSort {
public static void main(String[] args) {
List<String> list = new ArrayList<String>();
list.add("z");
list.add("a");
list.add("c");
list.add("b");
System.out.println("-------使用sort方法对List集合进行排序-----");
Collections.sort(list);
for (String string : list) {
System.out.println(string);
}
List<Book> bookList = new ArrayList<Book>();
bookList.add(new Book(12,"a" ,1));
bookList.add(new Book(14,"b" ,1));
bookList.add(new Book(13,"d" ,1));
bookList.add(new Book(15,"c" ,2));
bookList.add(new Book(16,"c" ,4));
Collections.sort(bookList, new BookComparator());
for (Book book : bookList) {
System.out.println(book.getId()+"--"+book.getPrice());
}
}
}
5.
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLrN2bsJEZlR3YhJHdu92Qvw1cy9GdhNWak5WSn5WaulGb0V3TvwVbvNmLzd2bsJmbj5ycldWYtl2Lc9CX6MHc0RHaiojIsJye.gif)
/**
* Collection接口中的toArray方法,转数组
* Arrays工具类中的asList方法,转集合
* @author Administrator
*
*/
public class Demo {
public static void main(String[] args) {
//集合转数组
List<String> list= new ArrayList<String>();
String[] ss = new String[list.size()];
list.toArray(ss);
String[] ss2 = list.toArray(new String[list.size()]);
//数组转集合
List<String> list2 = Arrays.asList(ss);
}
}
今天多一点积累,明天少一分烦恼