What ways can ensure that an object cannot be modified after initialization?

To make an object in Java immutable after initialization, you can use the following approaches:

• Declare the class as final so it cannot be subclassed and behavior cannot be overridden.
• Make all fields private final so they cannot be changed after assignment.
• Initialize all fields through the constructor.
• Do not provide setters (methods to modify fields).
• If fields are mutable objects (e.g., collections), return their copies or use immutable wrappers (e.g., Collections.unmodifiableList).

Example:

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

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

If there are collections:

private final List<String> items;

public ImmutableClass(List<String> items) {
    this.items = Collections.unmodifiableList(new ArrayList<>(items));
}

public List<String> getItems() {
    return items;
}

Thus, the object cannot be changed after creation.