Java - ObjectStreamField toString() method

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Description

The Java ObjectStreamField toString() method returns a string that describes this field.

• The toString() method returns a textual description of the field, including −

  • Field name

  • Field type

  • An optional unshared flag if applicable

• It's helpful for debugging, introspecting serialized fields, or generating simple logs.

Declaration

Following is the declaration for java.io.ObjectStreamField.toString() method.

public String toString()

Parameters

NA

Return Value

This method returns a string representation of the object.

Exception

NA

Example - Usage of ObjectStreamField toString() method

The following example shows the usage of ObjectStreamField toString() method.

ObjectStreamFieldDemo.java

package com.tutorialspoint;

import java.io.ObjectStreamClass;
import java.io.ObjectStreamField;
import java.util.Calendar;

public class ObjectStreamFieldDemo {
   public static void main(String[] args) {
   
      // create a new object stream class for Integers
      ObjectStreamClass osc = ObjectStreamClass.lookup(Integer.class);

      // get the field value from Integer class
      ObjectStreamField field = osc.getField("value");

      // print field as a string
      System.out.println("" + field.toString());

      // create a new object stream class for calendar
      ObjectStreamClass osc2 = ObjectStreamClass.lookup(Calendar.class);

      // get the field value from Integer class
      ObjectStreamField field2 = osc2.getField("isSet");

      // print field as a string
      System.out.println("" + field2.toString());
   }
}

Output

Let us compile and run the above program, this will produce the following result −

I value
[Z isSet

Example - Print toString() for each serializable field in a class

The following example shows the usage of ObjectStreamField toString() method. We're printing all serializable fields of a User class using ObjectStreamField.toString().

ObjectStreamFieldDemo.java

package com.tutorialspoint;

import java.io.ObjectStreamClass;
import java.io.ObjectStreamField;
import java.io.Serializable;

public class ObjectStreamFieldDemo {
   public static void main(String[] args) {
      ObjectStreamClass osc = ObjectStreamClass.lookup(User.class);
      ObjectStreamField[] fields = osc.getFields();

      System.out.println("Fields in User class:");
      for (ObjectStreamField field : fields) {
         System.out.println(" - " + field.toString());
      }
   }

   static class User implements Serializable {
      private static final long serialVersionUID = 1L;
      String username;
      int age;
      transient String password;  // not serialized
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Fields in User class:
 - I age
 - Ljava/lang/String; username

Explanation

• toString() automatically formats the field name and type.

• The transient field password is not shown, because it is not part of serialization.

Example - Create custom fields and call toString() directly

The following example shows the usage of ObjectStreamField toString() method. We're manually create ObjectStreamField instances and call toString().

ObjectStreamFieldDemo.java

package com.tutorialspoint;

import java.io.ObjectStreamField;

public class ObjectStreamFieldDemo {
   public static void main(String[] args) {
      ObjectStreamField field1 = new ObjectStreamField("id", int.class);
      ObjectStreamField field2 = new ObjectStreamField("name", String.class);
      ObjectStreamField field3 = new ObjectStreamField("active", boolean.class);

      System.out.println("Manually created fields:");
      System.out.println(" - " + field1.toString());
      System.out.println(" - " + field2.toString());
      System.out.println(" - " + field3.toString());
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Manually created fields:
 - I id
 - Ljava/lang/String; name
 - Z active

Explanation

• toString() clearly identifies each field's type and name.

• This is useful when building or analyzing custom serialization metadata.