Transient Variable

The keyword transient in Java used to indicate that the variable should not be serialized. By default all the variables in the object is converted to persistent state. In some cases, you may want to avoid persisting some variables because you don’t have the necessity to transfer across the network. So, you can declare those variables as transient. If the variable is declared as transient, then it will not be persisted. It is the main purpose of the transient keyword.

Look into the following example to understand the purpose of transient keyword:

package learnwebfws.samples;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

class NameStore implements Serializable{
private String firstName;
private transient String middleName;
private String lastName;
public NameStore (String fName,
                         String mName,
                         String lName){
this.firstName = fName;
this.middleName = mName;
this.lastName = lName;
}
public String toString(){
StringBuffer sb = new StringBuffer(40);
sb.append("First Name : ");
sb.append(this.firstName);
sb.append("Middle Name : ");
sb.append(this.middleName);
sb.append("Last Name : ");
sb.append(this.lastName);
return sb.toString();
}
}
public class TransientExample{
public static void main(String args[]) throws Exception {
NameStore nameStore = new NameStore("Steve",
                                     "Middle","Jobs");
ObjectOutputStream o = new ObjectOutputStream
                   (new FileOutputStream("nameStore"));
// writing to object
o.writeObject(nameStore);
o.close();

// reading from object
ObjectInputStream in =new ObjectInputStream(
                new FileInputStream("nameStore"));
NameStore nameStore1 = (NameStore)in.readObject();
System.out.println(nameStore1);
}
}

 // output will be :
First Name : Steve
Middle Name : null
Last Name : Jobs

 In the above example, the variable middle Name is declared as transient, so it will not be stored in the persistent storage. You can run the above example and check the results.