Java.io.ObjectInputStream getField.defaulted() 方法

描述

java.io.ObjectInputStream.getField.defaulted(String name) 方法跳過位元組。

宣告

以下是 java.io.ObjectInputStream.getField.defaulted() 方法的宣告。

public abstract boolean defaulted(String name)

引數

name - 欄位的名稱。

返回值

如果且僅當命名欄位為預設值時，此方法返回 true。

異常

• IOException - 如果從底層 InputStream 讀取時發生 I/O 錯誤。

• IllegalArgumentException - 如果 name 不對應於可序列化的欄位。

示例

以下示例演示了 java.io.ObjectInputStream.getField.defaulted() 方法的使用。

package com.tutorialspoint;

import java.io.*;

public class ObjectInputStreamDemo implements Serializable {
   public static void main(String[] args) {
      try {
         // create a new file with an ObjectOutputStream
         FileOutputStream out = new FileOutputStream("test.txt");
         ObjectOutputStream oout = new ObjectOutputStream(out);

         // write something in the file
         oout.writeObject(new Example());
         oout.flush();
         oout.close();

         // create an ObjectInputStream for the file we created before
         ObjectInputStream ois = new ObjectInputStream(new FileInputStream("test.txt"));

         // read an object from the stream and cast it to Example
         Example a = (Example) ois.readObject();

         // get if variable string is default in Example class
         System.out.println("" + a.isDefault);

         // print the string of a
         System.out.println("" + a.string);

      } catch (Exception ex) {
         ex.printStackTrace();
      }
   }

   static public class Example implements Serializable {
      static String string = "Hello World!";
      static boolean isDefault;
	  
      // assign a new serialPersistentFields 
      private static final ObjectStreamField[] serialPersistentFields = {
         new ObjectStreamField("string", String.class)
      };

      // create a custom readObject method
      private void readObject(ObjectInputStream in)
         throws IOException, ClassNotFoundException {

         // get the field and assign it at string variable
         ObjectInputStream.GetField fields = in.readFields();

         // check if string is defaulted, meaning if it has no value
         isDefault = fields.defaulted("string");
         string = (String) fields.get("string", null);
      }
	  
      // create a custom writeObject method
      private void writeObject(ObjectOutputStream out) throws IOException {

         // write into the ObjectStreamField array the variable string
         ObjectOutputStream.PutField fields = out.putFields();
         fields.put("string", string);
         out.writeFields();
         
      }
   }
}

讓我們編譯並執行上述程式，這將產生以下結果：

false
Hello World!