How are final objects created in Java?

There are two ways to create final objects in Java: declare a final variable or declare a class using the final modifier. When you declare a final variable, the object is created through an initializer; when you declare a final class, the class instance is immutable. Importantly, references to final objects can still change, but the objects they point to are immutable.

How to create final objects in Java

In Java, the final keyword is used to declare immutable objects. This means that once a final object is created, it is impossible to change its state. This is useful for creating thread-safe classes and preventing accidental modification of sensitive data.

There are two main ways to create a final object:

1. Declare a final variable

The simplest way is to declare a final variable and Initialized as an object:

public class FinalObjectExample {

    private final String name;

    public FinalObjectExample(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

}

2. Use the final modifier to declare the class

Another method is to use the final modifier to declare the entire class. This means that instances of the class are immutable:

public final class ImmutableClass {

    private final String value;

    public ImmutableClass(String value) {
        this.value = value;
    }

    public String getValue() {
        return value;
    }

}

The important thing to remember is that a reference to a final object can still be mutable itself. This means that you can assign a reference to a final object to a different variable:

FinalObjectExample obj1 = new FinalObjectExample("John");
FinalObjectExample obj2 = obj1;

obj2.getName(); // 返回 "John"

However, you still cannot modify the object pointed to by the obj1 or obj2 reference.

Practical case

Consider a class used to store sensitive data:

public class SensitiveData {

    private final int id;
    private final String value;

    public SensitiveData(int id, String value) {
        this.id = id;
        this.value = value;
    }

    public int getId() {
        return id;
    }

    public String getValue() {
        return value;
    }

}

By declaring the class final, we can ensure that the data is created remains unchanged, thereby improving security.

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