308 lines
9.0 KiB
Markdown
308 lines
9.0 KiB
Markdown
# 集合：
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**总结：**
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<img src="https://gitee.com/icecat2233/picture/raw/master/20250417165937735.png" alt="image-20250417165922953" style="zoom:50%;" />
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其中Collection接口中又分为**set**接口和**list**接口
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## Collection:
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<img src="https://gitee.com/icecat2233/picture/raw/master/20250417165721995.png" alt="image-20250417165713561" style="zoom:50%;" />
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**注意事项：**
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remove and contains方法依赖于底层equals方法
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## 集合通用遍历方法：
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### 1.迭代器 2.增强for循环 3.forEach
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首先获取迭代器：
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`Iterator<Student> it = c.iterator();`
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其次判断循环是否还有元素
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`hasNext()方法` `next()方法`
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注意：next()方法只调用一次，要不然会引起指针异常
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### 迭代器源码解析：
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### **三种方法演示：**
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```java
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public class Test2 {
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public static void main(String[] args) {
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Collection<Student> c = new ArrayList<>();
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c.add(new Student("小鸟游六花",15));
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c.add(new Student("小鸟游七花",15));
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c.add(new Student("小鸟游八花",15));
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//迭代器循环
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Iterator<Student> it = c.iterator();
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while (it.hasNext()){
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Student stu = it.next();
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System.out.println(stu.getName()+"---"+stu.getAge());
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}
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//增强for循环
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for (Student stu:c){
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System.out.println(stu);
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}
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//forEach遍历
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c.forEach(student -> System.out.println(student));
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}
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}
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```
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# List集合
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## list集合特点以及方法
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<img src="https://gitee.com/icecat2233/picture/raw/master/20250425155619805.png" alt="image-20250425155604336" style="zoom:67%;" />
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## 并发修改异常：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20250425154636875.png" alt="image-20250425154628294" style="zoom: 80%;" />
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<img src="https://gitee.com/icecat2233/picture/raw/master/20250425155719001.png" alt="image-20250425155717100" style="zoom:80%;" />
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## List集合的5种遍历方式
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1. Iterator迭代器
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251221153337614.png" alt="image-20251221153329358" style="zoom:50%;" />
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2. 增强for循环
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```Java
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//增强for循环
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//for(元素类型，起名 : 遍历的集合)
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for (Student stu : c) {
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System.out.println(stu);
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}
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```
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3. foreach
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```Java
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//foreach循环
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c.forEach(stu -> System.out.println(stu));
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```
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4. 普通for循环
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5. ListIterator迭代器
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# 数据结构：栈 队列 链表 数组
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<img src="https://gitee.com/icecat2233/picture/raw/master/20250425163326284.png" alt="image-20250425163323615" style="zoom: 67%;" />
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## 其中Arraylist集合扩容机制为
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1. 在初始化时长度为0
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2. 调用添加方法add时长度为10
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3. 此后长度超过10时，会将数组长度增加原来的1/2
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#### **源码分析**：**此为长度还未超出10时的源码过程**
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#### **此为超出10时源码过程**：
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## LinkedList特有方法
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removeFirst() removeLast()
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# Set集合
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251220175508010.png" alt="image-20251220175506487" style="zoom:67%;" />
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## 数据结构：树
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树的知识点总结：
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## 三种二叉树
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## 平衡二叉树
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<img src="https://gitee.com/icecat2233/picture/raw/master/20250509183513481.png" alt="image-20250509183446340" style="zoom: 50%;" />
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## 红黑树(重难点)
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红黑树是一种特殊的平衡二叉树，但并不是完全平衡的平衡二叉树，效率最高
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**添加树的情况**
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## TreeSet集合
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**排序和取出顺序示例：**
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**自然排序示例：**
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比较器排序示例：
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### **注意：**
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**this - 0 正序 o-this 降序**
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**o1 - o2 正序，o2 - o1 降序**
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<img src="https://gitee.com/icecat2233/picture/raw/master/20250510170601190.png" alt="image-20250510170600150" style="zoom: 67%;" />
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<img src="https://gitee.com/icecat2233/picture/raw/master/20250510170515008.png" alt="image-20250510170513793" style="zoom:50%;" />
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两种方式比较：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20250510170101423.png" alt="image-20250510170052265" style="zoom:67%;" />
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# HashSet
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## 基本运用：
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特点：去重（hashCode方法和equals方法共同运用）
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遍历：迭代器，增强for循环，foreach方法
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## **HashSet组成：**
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251220165008373.png" alt="image-20251220165000000" style="zoom:67%;" />
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## **JDK8版本以后Hashset的添加过程（面试常问重点！）**
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### **2**步骤过程：
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**将数值调用hashCode方法得到原始哈希值，然后将原始哈希值向右移动16位与原始哈希值进行异或操作，得到的数值与数组长度作取模运算得到位置。**
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251220165204636.png" alt="image-20251220165202216" style="zoom:67%;" />
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## 如何提高HashSet查询过程：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251220165544826.png" alt="image-20251220165543271" style="zoom:67%;" />
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## LinkedHashSet集合
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## 特点：
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**有序**，不重复，无索引，保证存取顺序。
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# 集合总结：
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# 小知识点：可变参数
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可变参数用在形参中可以接受多个数据。
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例：`int... 名称`；
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传输参数非常灵活，方便，可以不传参数，可以传1个或多个，也可以传数组
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**方法本质就是一个数组**
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# Collections集合工具类：
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示例：
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```java
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//多数据添加
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TreeSet<Student> alist = new TreeSet<>();
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Collections.addAll(alist,new Student("张三",14),new Student("八奈见杏菜",16),new Student("七奈见杏菜",16));
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System.out.println(alist);
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//二分查找
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ArrayList<String> ts = new ArrayList<>();
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Collections.addAll(ts,"2","3","4");
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System.out.println(Collections.binarySearch(ts, "2"));
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//洗牌
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ArrayList<Student> blist = new ArrayList<>();
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Collections.shuffle(blist);
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System.out.println(alist);
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//从集合中找最值
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System.out.println(Collections.max(ts));
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System.out.println(Collections.min(ts));
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System.out.println(Collections.min(alist));
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System.out.println(Collections.max(alist));
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```
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# MAP集合：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251220201802981.png" alt="image-20251220201801335" style="zoom:67%;" />
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## 常用API：
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251220201935518.png" alt="image-20251220201929102" style="zoom:67%;" />
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## MAP特点：
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## Map的三种遍历方式
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### 1：entrySet方法
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<img src="https://gitee.com/icecat2233/picture/raw/master/20251220205849706.png" alt="image-20251220205848087" style="zoom:50%;" />
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```java
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HashMap<String, String> m = new HashMap<>();
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m.put("杏菜", "15岁");
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m.put("佳树", "14岁");
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m.put("温水", "15岁");
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m.put("梦子", "15岁");
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//用entrySet方法获取到所有键值对象
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Set<Map.Entry<String, String>> entrySet = m.entrySet();
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//遍历set集合获取到每一个键值对儿对象
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for (Map.Entry<String, String> stringStringEntry : entrySet) {
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//通过键值对对象获取每一个数值
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System.out.println(stringStringEntry.getKey() + "---" + stringStringEntry.getValue());
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}
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```
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### 2：foreach方法：
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```Java
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hs.forEach(new BiConsumer<String, List<String>>() {
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@Override
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public void accept(String key, List<String> value) {
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System.out.print(key+"=");
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List list = value;
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for (int i = 0; i < list.size()-1; i++) {
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System.out.print(list.get(i)+",");
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}
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System.out.println(list.get(value.size()-1));
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}
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});
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```
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### 3:调用keyset方法获取所有键值
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