1. 集合 ---（原文链接：https://blog.csdn.net/B_evan/article/details/80611522）
(1). 集合类存放于java.util包中。
(2). 集合类型主要有3种：set(集）、list(列表）和map(映射)。
(3). 集合存放的都是对象的引用，而非对象本身。所以我们称集合中的对象就是集合中对象的引用。
简单来讲：集合就是一个放数据的容器，准确的说是放数据对象引用的容器。
2. 框架结构
3. Collection
public class CollDemo {
public static void main(String[] args) {
Collection collection = new ArrayList();
System.out.println(collection.getClass());
collection.add("a");
collection.add("a");
collection.add("b");
collection.add("abc");
System.out.println(collection);
System.out.println(collection.contains("abc"));
collection.remove("a");
System.out.println(collection);
collection.clear();
System.out.println(collection);
System.out.println(collection.isEmpty());
}
}
4. List
特点：有序，可重复
(1). List
public class ListDemo {
public static void main(String[] args) {
List list = new ArrayList();
System.out.println(list.getClass());
list.add("a");
list.add("a");
list.add("b");
list.add("abc");
System.out.println(list);
list.set(1, "b");
System.out.println(list);
list.remove(2);
System.out.println(list);
System.out.println(list.indexOf("a"));
}
}
(2). ArrayList
public class ArrayListDemo {
public static void main(String[] args) {
ArrayList arrayList = new ArrayList();
arrayList.add("a");
arrayList.add("a");
arrayList.add("b");
arrayList.add("abc");
Iterator iterator = arrayList.iterator();
while (iterator.hasNext()) {
String s1 = (String) iterator.next();
System.out.println(s1);
}
}
}
(3). LinkedList
public class LinkedListDemo {
public static void main(String[] args) {
LinkedList linkedList = new LinkedList();
linkedList.add("a");
linkedList.addFirst("b");
linkedList.offerFirst("c");
System.out.println(linkedList);
System.out.println(linkedList);
System.out.println(linkedList.removeFirst());
System.out.println(linkedList.removeLast());
System.out.println(linkedList);
System.out.println(linkedList.pollFirst());
System.out.println(linkedList.pollLast());
System.out.println(linkedList);
for (int i = 0; i < 5; i++) {
linkedList.add((char)(97+i));
}
System.out.println(linkedList);
System.out.println(linkedList.pollFirst());
System.out.println(linkedList.pollLast());
System.out.println(linkedList);
}
}
5. Set
特点：无序，不可重复
(1). HashSet
public class HashSetDemo {
public static void main(String[] args) {
HashSet hashSet = new HashSet();
Student s1 = new Student("111", 111);
Student s2 = new Student("222", 222);
Student s3 = new Student("333", 333);
Student s4 = new Student("111", 111);
hashSet.add(s1);
hashSet.add(s2);
hashSet.add(s3);
hashSet.add(s4);
System.out.println(hashSet);
Iterator iterator = hashSet.iterator();
while(iterator.hasNext()) {
Student st = (Student)iterator.next();
System.out.print(st.name + " ");
}
}
}
(2). TreeSet
public class TreeSetDemo {
public static void main(String[] args) {
TreeSet treeSet = new TreeSet();
treeSet.add(new Student("111", 111));
treeSet.add(new Student("222", 333));
treeSet.add(new Student("333", 333));
System.out.println(treeSet);
}
}
6. Map
特点：映射关系(键值对组成)，双列集合
(1). HashMap
public class HashMapDemo {
public static void main(String[] args) {
HashMap<String, Integer> hashMap = new HashMap<String, Integer>();
hashMap.put("张三", 20);
hashMap.put("李四", 30);
hashMap.put("王五", 40);
hashMap.put("赵六", 50);
System.out.println(hashMap);
System.out.println(hashMap.put("张三", 40));
System.out.println(hashMap);
System.out.println(hashMap.get("张三"));
System.out.println(hashMap.size());
Set<String> keySet = hashMap.keySet();
System.out.println(keySet);
Set<Map.Entry<String, Integer>> entrySet = hashMap.entrySet();
Iterator<Map.Entry<String, Integer>> iterator = entrySet.iterator();
while(iterator.hasNext()) {
Map.Entry<String, Integer> entry = iterator.next();
System.out.println(entry.getKey() + ", " + entry.getValue());
}
}
}
7. Iterator
Java迭代器Iterator是 Java 集合框架中的一种机制，它提供了一种在不暴露集合内部实现的情况下遍历集合元素的方法。
public class RunoobTest {
public static void main(String[] args) {
// 创建集合
ArrayList<String> sites = new ArrayList<String>();
sites.add("Google");
sites.add("Runoob");
sites.add("Taobao");
sites.add("Zhihu");
// 获取迭代器
Iterator<String> it = sites.iterator();
// 输出集合中的所有元素
while(it.hasNext()) {
System.out.println(it.next());
}
}
}
8. 泛型 -- 泛指（不具体）的类型
(1). 避免了强制类型转换
(2). 将运行时ClassCastException异常转到了编译阶段
public class GenericDemo02 {
public static void main(String[] args) {
ArrayList<String> arrayList01 = new ArrayList<>();
arrayList01.add("a");
arrayList01.add("b");
ArrayList<Integer> arrayList02 = new ArrayList<>();
arrayList02.add(1);
arrayList02.add(2);
}
private static void m1(ArrayList<String> arrayList) {
Iterator<String> iterator = arrayList.iterator();
while(iterator.hasNext()) {
String str = iterator.next();
System.out.println(str);
}
}
}
9. Lambda表达式
public class LambdaDemo {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<>();
arrayList.add("zhangsan");
arrayList.add("lisi");
arrayList.add("wangwu");
arrayList.add("zhaoliu");
arrayList.sort((o1, o2) -> {
System.out.println(o1.compareTo(o2));
return o1.compareTo(o2);
});
System.out.println(arrayList);
}
}
标签：System,println,add,集合,new,public,out From： https://www.cnblogs.com/jiuxis/p/17235559.html