例子
以下示例显示java.io.ObjectInputStream.getField.defaulted()方法的用法。
package com.jc2182;
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();
}
}
}
让我们编译并运行以上程序，这将产生以下结果-
