Inheritance allows a child class to acquire properties and methods from a parent class.

It is used for code reuse and for modeling an is-a relationship.

Example

class BaseJob {
    void recordStart() { System.out.println("Job started"); }
}

class DataExportJob extends BaseJob {
    void writeCsv() { System.out.println("Writing CSV"); }
}

DataExportJob inherits recordStart() from BaseJob.

Why Inheritance Is Used

• Reduce duplicated code.
• Reuse common behavior.
• Organize related classes.
• Enable runtime polymorphism through overriding.

Types of Inheritance

Single

BaseJob -> DataExportJob

Multilevel

BaseJob -> DataExportJob -> ScheduledDataExportJob

Hierarchical

BaseJob -> DataExportJob
BaseJob -> CleanupJob

Multiple

Java does not support multiple inheritance with classes because it can create ambiguity. Java supports multiple inheritance of capability through interfaces.

What Is Inherited?

A child inherits non-private fields and methods.

Constructors are not inherited.

Is-A Rule

Use inheritance when the child truly is a parent type.

• A scheduled export is a data export: potentially a good fit.
• An export job is a CSV writer: wrong; use composition instead.

Interview Notes

• Inheritance represents an is-a relationship.
• It allows reuse of parent behavior.
• Method overriding lets child classes customize inherited behavior.
• Use inheritance carefully; wrong hierarchies create fragile code.