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                # 如何在 java 中序列化`HashMap` > 原文: [https://beginnersbook.com/2013/12/how-to-serialize-hashmap-in-java/](https://beginnersbook.com/2013/12/how-to-serialize-hashmap-in-java/) `HashMap`類默認是序列化的,這意味著我們不需要實現`Serializable`接口,以使其符合序列化的條件。在本教程中,我們將學習**如何編寫`HashMap`對象及其內容到文件**和**如何從文件中讀取`HashMap`對象**。在分享完整代碼之前,讓我簡單介紹一下序列化和反序列化。 序列化:這是一個將`Object`與其屬性和內容一起寫入文件的過程。它在內部以字節流轉換對象。 反序列化:這是一個從文件中讀取`Object`及其屬性以及`Object`內容的過程。 #### 示例: **`HashMap`的序列化:**在下面的類中,我們將`HashMap`內容存儲在`hashmap.ser`序列化文件中。運行以下代碼后,它將生成一個`hashmap.ser`文件。此文件將在下一個類中用于反序列化。 ```java package beginnersbook.com; import java.io.*; import java.util.HashMap; public class Details { public static void main(String [] args) { HashMap<Integer, String> hmap = new HashMap<Integer, String>(); //Adding elements to HashMap hmap.put(11, "AB"); hmap.put(2, "CD"); hmap.put(33, "EF"); hmap.put(9, "GH"); hmap.put(3, "IJ"); try { FileOutputStream fos = new FileOutputStream("hashmap.ser"); ObjectOutputStream oos = new ObjectOutputStream(fos); oos.writeObject(hmap); oos.close(); fos.close(); System.out.printf("Serialized HashMap data is saved in hashmap.ser"); }catch(IOException ioe) { ioe.printStackTrace(); } } } ``` 輸出: ```java Serialized HashMap data is saved in hashmap.ser ``` **反序列化:**這里我們正在重現`HashMap`對象,它是我們通過運行上面的代碼創建的序列化文件的內容。 ```java package beginnersbook.com; import java.io.*; import java.util.HashMap; import java.util.Map; import java.util.Iterator; import java.util.Set; public class Student { public static void main(String [] args) { HashMap<Integer, String> map = null; try { FileInputStream fis = new FileInputStream("hashmap.ser"); ObjectInputStream ois = new ObjectInputStream(fis); map = (HashMap) ois.readObject(); ois.close(); fis.close(); }catch(IOException ioe) { ioe.printStackTrace(); return; }catch(ClassNotFoundException c) { System.out.println("Class not found"); c.printStackTrace(); return; } System.out.println("Deserialized HashMap.."); // Display content using Iterator Set set = map.entrySet(); Iterator iterator = set.iterator(); while(iterator.hasNext()) { Map.Entry mentry = (Map.Entry)iterator.next(); System.out.print("key: "+ mentry.getKey() + " & Value: "); System.out.println(mentry.getValue()); } } } ``` 輸出: ```java Deserialized HashMap.. key: 9 & Value: GH key: 2 & Value: CD key: 11 & Value: AB key: 33 & Value: EF key: 3 & Value: IJ ``` #### 參考: * [`HashMap`文檔](https://docs.oracle.com/javase/7/docs/api/java/util/HashMap.html) * [`Serializable` javadoc](https://docs.oracle.com/javase/1.5.0/docs/api/java/io/Serializable.html) * [`ObjectOutputStream` javadoc](https://docs.oracle.com/javase/7/docs/api/java/io/ObjectOutputStream.html) * [`ObjectInputStream`文檔](https://docs.oracle.com/javase/7/docs/api/java/io/ObjectInputStream.html) * [`FileInputStream`](https://docs.oracle.com/javase/7/docs/api/java/io/FileInputStream.html) * [`FileOutputStream`](https://docs.oracle.com/javase/7/docs/api/java/io/FileOutputStream.html)
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