java theories access modifiers

Java Access Modifiers

Introduction

Access modifiers in Java control where classes, attributes, methods, and constructors can be accessed.

Java provides four access levels:

1. public
2. private
3. protected
4. Default or package-private access

Access modifiers help to protect data, prevent unwanted changes, support encapsulation, and make code easier to maintain.

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Access Modifier Syntax

An access modifier is written before an attribute or method.

accessModifier dataType attributeName;

Example:

private String patientName;

Method example:

public String getPatientName() {
    return patientName;
}

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Public Access Modifier

The public modifier allows access from any class and any package.

public String getPatientCode() {
    return patientCode;
}

HMIS-style action method:

public void processReport() {
    // Generate report
}

Use public for:

• Getter methods
• Setter methods
• Controller action methods
• Service methods
• Facade methods
• Methods that must be accessed by other packages

Public attributes are usually not recommended:

public String patientCode;

Prefer a private attribute with public getters and setters:

private String patientCode;

public String getPatientCode() {
    return patientCode;
}

public void setPatientCode(String patientCode) {
    this.patientCode = patientCode;
}

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Private Access Modifier

The private modifier allows access only inside the same class.

private String patientName;
private Department department;
private Investigation investigation;

Private helper method:

private boolean isDateRangeValid() {
    return fromDate != null
            && toDate != null
            && !fromDate.after(toDate);
}

Use private for:

• Attributes
• Internal helper methods
• Validation methods
• Query-building methods
• Sensitive information

Private attributes help to:

• Protect internal data
• Prevent direct modification
• Support validation through setters
• Reduce errors
• Support encapsulation

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Protected Access Modifier

The protected modifier allows access:

• Inside the same class
• Inside the same package
• Inside child classes

HMIS-style example:

@Override
protected EntityManager getEntityManager() {
    return entityManager;
}

Facade example:

@Stateless
public class PatientInvestigationFacade
        extends AbstractFacade<PatientInvestigation> {

    @PersistenceContext(unitName = "hmisPU")
    private EntityManager entityManager;

    @Override
    protected EntityManager getEntityManager() {
        return entityManager;
    }
}

Use protected when inheritance requires access to a method.

Prefer private attributes with protected methods:

private EntityManager entityManager;

protected EntityManager getEntityManager() {
    return entityManager;
}

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Default Access Modifier

When no access modifier is written, Java uses default access.

Default access is also called:

• Package-private access
• Package access
• No-modifier access

Example:

String internalCode;

Method example:

void clearTemporaryData() {
}

A default member can only be accessed by classes in the same package.

HMIS-style example:

package com.divudi.bean.lab;

class LabReportHelper {

    void prepareData() {
        // Internal package logic
    }
}

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Access Modifier Comparison

Modifier	Same class	Same package	Child class in another package	Other packages
private	Yes	No	No	No
Default	Yes	Yes	No	No
protected	Yes	Yes	Yes	No
public	Yes	Yes	Yes	Yes

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Access Modifiers for Attributes

Attributes should normally be private.

Recommended:

private String patientCode;
private Date createdAt;
private Department department;
private boolean retired;

Avoid:

public String patientCode;
public Date createdAt;

Use public getters and setters:

public String getPatientCode() {
    return patientCode;
}

public void setPatientCode(String patientCode) {
    this.patientCode = patientCode;
}

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Access Modifiers for Methods

Public method

public void process() {
}

Can be called by other classes or XHTML pages.

Private method

private boolean validateFilters() {
    return fromDate != null && toDate != null;
}

Can only be called inside the same class.

Protected method

protected EntityManager getEntityManager() {
    return entityManager;
}

Can be called by child classes and classes in the same package.

Default method

void resetInternalState() {
}

Can be called only from the same package.

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Access Modifiers for Classes

A top-level Java class can normally use:

• public
• Default access

Public class:

public class InvestigationReport {
}

Default-access class:

class InvestigationReportHelper {
}

A top-level class cannot be declared private or protected.

Inner classes may use private, protected, or public.

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Encapsulation with Access Modifiers

Encapsulation means keeping attributes private and accessing them through methods.

public class BillData {

    private double total;
    private double discount;

    public double getTotal() {
        return total;
    }

    public void setTotal(double total) {
        if (total < 0) {
            throw new IllegalArgumentException(
                    "Total cannot be negative"
            );
        }

        this.total = total;
    }

    public double getDiscount() {
        return discount;
    }

    public void setDiscount(double discount) {
        if (discount < 0) {
            throw new IllegalArgumentException(
                    "Discount cannot be negative"
            );
        }

        this.discount = discount;
    }

    public double calculateNetTotal() {
        return total - discount;
    }
}

In this example:

• total and discount are private.
• Getters provide read access.
• Setters provide controlled write access.
• Validation prevents invalid values.
• calculateNetTotal() is public behaviour.

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HMIS-Style Example

public class InvestigationReportData {

    private Date fromDate;
    private Date toDate;
    private Department laboratory;
    private Investigation investigation;

    private List<PatientInvestigation> results =
            new ArrayList<>();

    public Date getFromDate() {
        return fromDate;
    }

    public void setFromDate(Date fromDate) {
        this.fromDate = fromDate;
    }

    public Date getToDate() {
        return toDate;
    }

    public void setToDate(Date toDate) {
        this.toDate = toDate;
    }

    public Department getLaboratory() {
        return laboratory;
    }

    public void setLaboratory(Department laboratory) {
        this.laboratory = laboratory;
    }

    public Investigation getInvestigation() {
        return investigation;
    }

    public void setInvestigation(
            Investigation investigation) {
        this.investigation = investigation;
    }

    public List<PatientInvestigation> getResults() {
        return results;
    }

    public void process() {
        results.clear();

        if (!isDateRangeValid()) {
            return;
        }

        loadResults();
    }

    private boolean isDateRangeValid() {
        return fromDate != null
                && toDate != null
                && !fromDate.after(toDate);
    }

    private void loadResults() {
        // Load report results
    }
}

Access modifiers used

Member	Modifier	Reason
Attributes	private	Protect internal data
Getters	public	Allow controlled reading
Setters	public	Allow controlled updating
process()	public	Called from another component or XHTML
isDateRangeValid()	private	Internal validation
loadResults()	private	Internal processing

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Sensitive Data and Access Modifiers

HMIS contains sensitive patient and healthcare information.

private String patientName;
private String nationalIdentityCardNumber;
private String diagnosis;
private String investigationResult;
private String prescriptionDetails;

Sensitive attributes should be private.

Avoid:

public String diagnosis;

Prefer:

private String diagnosis;

Only provide a public getter when the information must be accessed:

public String getDiagnosis() {
    return diagnosis;
}

Access modifiers alone do not provide full security. The application must also use authentication, authorization, role-based access, audit logging, and secure database access.

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Common Mistakes

Public attributes

Avoid:

public String patientName;

Use:

private String patientName;

Private method needed by XHTML

Incorrect:

private void process() {
}

Correct:

public void process() {
}

Public internal helper method

Avoid:

public boolean isDateRangeValid() {
}

when only the same class uses it.

Prefer:

private boolean isDateRangeValid() {
}

Protected attributes without a reason

Avoid:

protected Department department;

Prefer:

private Department department;

Using default access accidentally

String patientCode;

If the attribute should be private, write:

private String patientCode;

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Best Practices

1. Keep attributes private.
2. Use public getters and setters only when required.
3. Keep internal helper methods private.
4. Use protected methods only for inheritance.
5. Use default access only for package-level design.
6. Avoid public mutable attributes.
7. Do not expose sensitive patient information unnecessarily.
8. Use the smallest access level required.
9. Do not make everything public.
10. Review access levels when refactoring code.

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Summary

Java has four access levels:

private
default
protected
public

From most restricted to least restricted:

private → default → protected → public

Recommended HMIS usage:

private String patientCode;

public String getPatientCode() {
    return patientCode;
}

public void setPatientCode(String patientCode) {
    this.patientCode = patientCode;
}

private boolean validatePatientCode() {
    return patientCode != null
            && !patientCode.trim().isEmpty();
}

Important rules:

• Attributes should normally be private.
• Public methods provide controlled access.
• Private methods contain internal logic.
• Protected methods support inheritance.
• Default access limits members to the same package.
• Use the smallest access level necessary.