What is the role of transient keyword

The function of the transient keyword is: variables modified by transient do not participate in serialization and deserialization. When an object is serialized, the values ​​of transient variables are not included in the serialized representation, whereas non-transient variables are included.

The operating environment of this tutorial: windows7 system, java10 version, Dell G3 computer.

(Learning video sharing: java teaching video)

Java's serialization provides a mechanism for persisting object instances. When persisting an object, there may be a special object data member that we don't want to use the serialization mechanism to save.

To turn off serialization on a field of a specific object, you can add the keyword transient before this field.

When an object is serialized, the values ​​of transient variables are not included in the serialized representation, while non-transient variables are included.

In short, Variables modified by transient do not participate in serialization and deserialization.

Next, use code to prove it.

Create a new Student class to implement the Serializable interface, and rewrite its toString method to facilitate observation of the results.

An age attribute is not modified by transient, and a name attribute is modified by transient.

public class Student implements Serializable {
    private int age;
    private transient String name;

    public Student() {
    }

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

    @Override
    public String toString() {
        return "Student{" + "age=" + age + ", name='" + name + '\'' + '}';
    }

}

Then test it in the TransientTest class.

PS:

For the simplicity of the code, the IO operation here does not perform a try catch operation but is thrown directly.

public class TestTransient {

    public static void main(String[] args) throws Exception {
        // 实例化一个Student对象.
        Student student = new Student(15, "HuaGe");
        System.out.println(student);

        // 将student对象写入磁盘文件(序列化)
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("student.txt"));
        oos.writeObject(student);
        oos.close();

        // 从磁盘文件读取student对象(反序列化)
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("student.txt"));
        student = (Student) ois.readObject();
        System.out.println(student);
    }
}

Run the main method and observe the console printing information.

It was found that after serialization and deserialization, the name attribute changed from HuaGe to null.

This shows that is modified by transient Variables do not participate in serialization and deserialization.

Are there any exceptions?

We know that there are two serialization methods in java.

1. Implement the Serializable interface.

2. Implement the Externalizable interface.

Externalizable interface is a subclass of Serializable interface

The source code is as follows

public interface Externalizable extends java.io.Serializable {
 
    void writeExternal(ObjectOutput out) throws IOException;

   
    void readExternal(ObjectInput in) throws IOException, ClassNotFoundException;
}

The two methods of this interface can specify which attributes in the class are serialized.

When using this interface, no matter whether the properties are modified by transient or not,

no properties will be serialized by default. Therefore, classes that implement the Externalizable interface

generally no longer use transient modified attributes.

Summary:

1. Variables modified by transient do not participate in serialization and deserialization

#2. Transient is generally used in classes that implement the Serializable interface.

For more programming-related knowledge, please visit: Programming Teaching! !

The above is the detailed content of What is the role of transient keyword. For more information, please follow other related articles on the PHP Chinese website!