What is the 'transient' keyword in Java?

The transient keyword in Java is used to indicate that a class field should not be serialized when the object of that class is converted into a byte stream.

Usage:

• Exclusion from serialization: Fields marked as transient are ignored by standard serialization mechanisms (e.g., using ObjectOutputStream).
• Use cases:
  • Saving state that can be easily recalculated during deserialization (e.g., cached data).
  • Avoiding serialization of confidential information (passwords, tokens).
  • Excluding resources that cannot be serialized (e.g., input/output streams).

Example:

import java.io.Serializable;

class User implements Serializable {
    private String username;
    private transient String password; // This field will not be serialized
    private int age;

    public User(String username, String password, int age) {
        this.username = username;
        this.password = password;
        this.age = age;
    }

    // Getters and setters
}