JPA Creating an Entity

A Java class can be easily transformed into an entity. For transformation the basic requirements are: -

• No-argument Constructor
• Annotation

Here, we will learn how to transform a regular Java class into an entity class with the help of an example: -

Student class

public class Student {  
    private int id;  
    private String name;  
    private long fees;

    public Student() {}

    public Student(int id)   
      {  
        this.id = id;  
      }

    public int getId()   
     {  
        return id;  
     }  
    public void setId(int id)    
     {  
        this.id = id;  
     }  
    public String getName()  
     {  
        return name;   
     }  
    public void setName(String name)   
     {  
        this.name = name;  
      }  
    public long getFees()  
     {  
        return fees;  
      }  
    public void setFees (long fees)  
     {  
        this.fees = fees;  
     }   
}  

Above class is a regular java class having three attributes id, name and fees. To transform this class into an entity, add @Entity and @Id annotation in it.

• @Entity - This is a marker annotation which indicates that this class is an entity. This annotation must be placed on the class name.
• @Id - This annotation is placed on a specific field that holds the persistent identifying properties. This field is treated as a primary key in database.

Student Entity Class

import javax.persistence.*; 

@Entity  
public class Student {  
    @Id  
    private int id;  
    private String name;  
    private long fees; 

    public Student() {} 

    public Student(int id)   
     {  
        this.id = id;  
     }

 
    public int getId()   
     {  
        return id;  
      }  
    public void setId(int id)   
     {  
        this.id = id;  
      }  
    public String getName()  
     {  
        return name;   
     }  
    public void setName(String name)   
     {  
        this.name = name;  
     }  
    public long getFees()  
     {  
        return fees;  
     }  
    public void setFees (long fees)  
     {  
        this.fees = fees;  
     }   
}