java.io.ObjectInputStream.getField.defaulted(String name) 方法跳過字節。

聲明

以下是java.io.ObjectInputStream.getField.defaulted()方法的聲明

public abstract boolean defaulted(String name)

參數

• name -- 該字段的名稱

返回值

此方法返回true，當且僅當指定的字段被缺省

異常

• IOException -- 如果從基礎InputStream讀取有I/O錯誤

• IllegalArgumentException -- 如果名稱不對應一個序列化字段

例子

下麵的示例演示java.io.ObjectInputStream.getField.defaulted()方法的用法。

package com.yiibai;

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();

      }
   }
}

讓我們編譯和運行上麵的程序，這將產生以下結果：

false
Hello World!