How can an immutable object be implemented in programming?

An immutable object is an object whose state cannot be changed after creation. In Java, this is achieved through several methods:

1. Declare the class as final — so it cannot be subclassed and behavior cannot be altered.
2. Make all fields private and final — so their values cannot be changed after initialization.
3. Do not provide setters — only getters for accessing fields.
4. Initialize all fields through the constructor.
5. If a field is a reference type, ensure its immutability (for example, by using immutable collections or creating copies of objects when passing them).

Example:

public final class Person {
    private final String name;
    private final int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

Thus, once a Person object is created, its state cannot be changed.