add to map

data/3.Java高阶/12.Apache Common/config.json

+{
+  "node_id": "java-e5d307b8ce2049648b4afd9fecdb48b0",
+  "keywords": []
+}
\ No newline at end of file

data/3.Java高阶/4.收集器/config.json

@@ -2,5 +2,9 @@
   "node_id": "java-0f1fc49b2e1c41368403ca2239810920",
   "keywords": [],
   "children": [],
-  "export": ["to_list.json"]
+  "export": [
+    "to_list.json",
+    "to_set.json",
+    "to_map.json"
+  ]
 }
\ No newline at end of file

data/3.Java高阶/4.收集器/to_map.json

+{
+  "type": "code_options",
+  "author": "刘鑫",
+  "source": "to_map.md",
+  "notebook_enable": false
+}
\ No newline at end of file

data/3.Java高阶/4.收集器/to_map.md

+# Stream To Map
+
+现有类型 Person 如下：
+
+```java
+public class Person{
+    private final int id;
+    private final String name;
+    public Person(int id, String name){
+        this.id = id;
+        this.name = name;
+    }
+    
+    public int getId(){
+        return id;
+    }
+    
+    public String getName(){
+        return name;
+    }
+}
+```
+
+下面的程序将 `Stream<Person> people` 中的数据整理到一个 Map<Integer, String> 字典中，键和值分别对应 Person 类型的 id 和name。其中有错的是：
+
+## 答案
+
+```java
+Map<Integer, String> dict = new Map();
+
+people.collect(p ->{
+    dict.put(p.getId(), p.getName());
+});
+```
+
+## 选项
+
+### 常规收集器
+
+```java
+Map<Integer, String> dict = people().collect(Collectors.toMap(Person::getId, Person::getName));
+```
+
+### 朴素的过程化方法
+
+```java
+Map<Integer, String> dict = new HashMap<>();
+people.forEach(p->{
+    dict.put(p.getId(), p.getName());
+});
+```
+
+### 朴素的 for 循环，不推荐但是能用
+
+```java
+Map<Integer, String> dict = new HashMap<>();
+for(var p: people.toList()){
+    dict.put(p.getId(), p.getName());
+}
+```