Java.io.ObjectInputStream.getField.defaulted()方法實例

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

下面的示例演示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面的程序，這將產生以下結果：

false Hello World!