遍历 Java 中的 HashMap
原文:https://www . geesforgeks . org/traverse-through-a-hashmap-in-Java/
HashMap 是 java collections 框架的一部分。它内部使用哈希技术。
这篇文章包含了遍历 HashMap 的不同方法，如下所示:
-
Using an Iterator: Iterator is an interface in java.util package which is used to iterate through a collection.
- hm.entrySet() 用于检索所有名为 Map 的键值对。在内部输入并存储到一个集合中。
- hm.entrySet()。iterator() 返回一个迭代器，该迭代器充当光标，指向集合的第一个元素，并一直移动到最后。
- hmIterator.hasNext() 检查集合中的下一个元素，并返回一个布尔值
- hmIterator.next() 返回下一个元素(Map。条目)从集合中删除。
- mapElement.getKey() 返回关联地图的键。进入
- mapElement.getValue() 返回关联地图的值。进入
示例:
```java // Java program to traverse through // a hashmap using iterator
import java.util.*;
class GfG { public static void main(String[] args) { // Consider the hashmap contains // student name and their marks HashMap hm = new HashMap();
// Adding mappings to HashMap hm.put("GeeksforGeeks", 54); hm.put("A computer portal", 80); hm.put("For geeks", 82);
// Printing the HashMap System.out.println("Created hashmap is" + hm);
// Getting an iterator Iterator hmIterator = hm.entrySet().iterator();
// Iterate through the hashmap // and add some bonus marks for every student System.out.println("HashMap after adding bonus marks:");
while (hmIterator.hasNext()) { Map.Entry mapElement = (Map.Entry)hmIterator.next(); int marks = ((int)mapElement.getValue() + 10); System.out.println(mapElement.getKey() + " : " + marks); } } } ```
Output:
```java Created hashmap is{GeeksforGeeks=54, A computer portal=80, For geeks=82} HashMap after adding bonus marks: GeeksforGeeks : 64 A computer portal : 90 For geeks : 92
```
-
使用进行每个循环 :
```java // Java program for traversing // through a hashmap using for-each loop
import java.util.*;
class GfG { public static void main(String[] args) {
// Consider the hashmap containing // student name and their marks HashMap hm = new HashMap();
// Adding mappings to HashMap hm.put("GeeksforGeeks", 54); hm.put("A computer portal", 80); hm.put("For geeks", 82);
// Printing the HashMap System.out.println("Created hashmap is" + hm);
// Loop through the hashmap System.out.println("HashMap after adding bonus marks:");
// Using for-each loop for (Map.Entry mapElement : hm.entrySet()) { String key = (String)mapElement.getKey();
// Add some bonus marks // to all the students and print it int value = ((int)mapElement.getValue() + 10);
System.out.println(key + " : " + value); } } } ```
输出:
```java Created hashmap is{GeeksforGeeks=54, A computer portal=80, For geeks=82} HashMap after adding bonus marks: GeeksforGeeks : 64 A computer portal : 90 For geeks : 92
```
-
使用 forEach() 方法: forEach()是在 java 8 中引入的 hashmap 方法。它用于遍历 hashmap，也减少了代码行数。
```java // Java program for traversing // through a hashmap using for-each loop
import java.util.*;
class GfG { public static void main(String[] args) {
// Consider the hashmap containing // student name and their marks HashMap hm = new HashMap();
// Adding mappings to HashMap hm.put("GeeksforGeeks", 54); hm.put("A computer portal", 80); hm.put("For geeks", 82);
// Printing the HashMap System.out.println("Created hashmap is" + hm);
// Loop through the hashmap // and add bonus marks System.out.println("HashMap after adding bonus marks:");
// Using Hashmap.forEach() hm.forEach((k, v) -> System.out.println(k + " : " + (v + 10))); } } ```
输出:
```java Created hashmap is{GeeksforGeeks=54, A computer portal=80, For geeks=82} HashMap after adding bonus marks: GeeksforGeeks : 64 A computer portal : 90 For geeks : 92
```
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