Home > Articles


This chapter is from the book

3.2 Method Declarations

For the purpose of this book, we will use the following simplified syntax of a method declaration:

method_modifiers return_type method_name
                                 (formal_parameter_list) throws_clause // Method header
{ // Method body

In addition to the name of the method, the method header can specify the following information:

  • Scope or accessibility modifier (§4.7, p. 123)

  • Additional method modifiers (§4.8, p. 131)

  • The type of the return value, or void if the method does not return any value (§6.4, p. 224)

  • A formal parameter list

  • Any exceptions thrown by the method, which are specified in a throws clause (§6.9, p. 251)

The formal parameter list is a comma-separated list of parameters for passing information to the method when the method is invoked by a method call (§3.5, p. 72). An empty parameter list must be specified by ( ). Each parameter is a simple variable declaration consisting of its type and name:

optional_parameter_modifier type parameter_name

The parameter names are local to the method (§4.4, p. 117). The optional parameter modifier final is discussed in §3.5, p. 80. It is recommended to use the @param tag in a Javadoc comment to document the formal parameters of a method.

The signature of a method comprises the name of the method and the types of the formal parameters only.

The method body is a block containing the local variable declarations (§2.3, p. 40) and the statements of the method.

The mandatory parts of a method declaration are the return type, the method name, and the method body braces ({}), as exemplified by the following method declaration:

void noAction() {}

Like member variables, member methods can be characterized as one of two types:

  • Instance methods, which are discussed later in this section

  • Static methods, which are discussed in §4.8, p. 132


Statements in Java can be grouped into various categories. Variable declarations with explicit initialization of the variables are called declaration statements (§2.3, p. 40, and §3.4, p. 60). Other basic forms of statements are control flow statements (§6.1, p. 200) and expression statements.

An expression statement is an expression terminated by a semicolon. Any value returned by the expression is discarded. Only certain types of expressions have meaning as statements:

  • Assignments (§5.6, p. 158)

  • Increment and decrement operators (§5.9, p. 176)

  • Method calls (§3.5, p. 72)

  • Object creation expressions with the new operator (§5.17, p. 195)

A solitary semicolon denotes the empty statement, which does nothing.

A block, {}, is a compound statement that can be used to group zero or more local declarations and statements (§4.4, p. 117). Blocks can be nested, since a block is a statement that can contain other statements. A block can be used in any context where a simple statement is permitted. The compound statement that is embodied in a block begins at the left brace, {, and ends with a matching right brace, }. Such a block must not be confused with an array initializer in declaration statements (§3.4, p. 60).

Labeled statements are discussed in §6.4 on page 220.

Instance Methods and the Object Reference this

Instance methods belong to every object of the class and can be invoked only on objects. All members defined in the class, both static and non-static, are accessible in the context of an instance method. The reason is that all instance methods are passed an implicit reference to the current object—that is, the object on which the method is being invoked. The current object can be referenced in the body of the instance method by the keyword this. In the body of the method, the this reference can be used like any other object reference to access members of the object. In fact, the keyword this can be used in any non-static context. The this reference can be used as a normal reference to reference the current object, but the reference cannot be modified—it is a final reference (§4.8, p. 133).

The this reference to the current object is useful in situations where a local variable hides, or shadows, a field with the same name. In Example 3.1, the two parameters noOfWatts and indicator in the constructor of the Light class have the same names as the fields in the class. The example also declares a local variable location, which has the same name as one of the fields. The reference this can be used to distinguish the fields from the local variables. At (1), the this reference is used to identify the field noOfWatts, which is assigned the value of the parameter noOfWatts. Without the this reference at (2), the value of the parameter indicator is assigned back to this parameter, and not to the field by the same name, resulting in a logical error. Similarly at (3), without the this reference, it is the local variable location that is assigned the value of the parameter site, and not the field with the same name.

Example 3.1 Using the this Reference

public class Light {
  // Fields:
  int     noOfWatts;      // Wattage
  boolean indicator;      // On or off
  String  location;       // Placement

  // Constructor
  public Light(int noOfWatts, boolean indicator, String site) {
    String location;

    this.noOfWatts = noOfWatts;   // (1) Assignment to field
    indicator = indicator;        // (2) Assignment to parameter
    location = site;              // (3) Assignment to local variable
    this.superfluous();           // (4)
    superfluous();                // equivalent to call at (4)

  public void superfluous() {
    System.out.printf("Current object: %s%n", this); // (5)

  public static void main(String[] args) {
    Light light = new Light(100, true, "loft");
    System.out.println("No. of watts: " + light.noOfWatts);
    System.out.println("Indicator:    " + light.indicator);
    System.out.println("Location:     " + light.location);

Probable output from the program:

Current object: Light@1bc4459
Current object: Light@1bc4459
No. of watts: 100
Indicator:    false
Location:     null

If a member is not shadowed by a local declaration, the simple name member is considered a short-hand notation for this.member. In particular, the this reference can be used explicitly to invoke other methods in the class. This usage is illustrated at (4) in Example 3.1, where the method superfluous() is called.

If, for some reason, a method needs to pass the current object to another method, it can do so using the this reference. This approach is illustrated at (5) in Example 3.1, where the current object is passed to the printf() method. The printf() method prints the string representation of the current object (which comprises the name of the class of the current object and the hexadecimal representation of the current object’s hash code). (The hash code of an object is an int value that can be used to store and retrieve the object from special data structures called hash tables.)

Note that the this reference cannot be used in a static context, as static code is not executed in the context of any object.

Method Overloading

Each method has a signature, which comprises the name of the method plus the types and order of the parameters in the formal parameter list. Several method implementations may have the same name, as long as the method signatures differ. This practice is called method overloading. Because overloaded methods have the same name, their parameter lists must be different.

Rather than inventing new method names, method overloading can be used when the same logical operation requires multiple implementations. The Java SE platform API makes heavy use of method overloading. For example, the class java.lang.Math contains an overloaded method min(), which returns the minimum of two numeric values.

public static double min(double a, double b)
public static float min(float a, float b)
public static int min(int a, int b)
public static long min(long a, long b)

In the following examples, five implementations of the method methodA are shown:

void methodA(int a, double b) { /* ... */ }      // (1)
int  methodA(int a)           { return a; }      // (2)
int  methodA()                { return 1; }      // (3)
long methodA(double a, int b) { return b; }      // (4)
long methodA(int x, double y) { return x; }      // (5) Not OK.

The corresponding signatures of the five methods are as follows:

methodA(int, double)             1'
methodA(int)                     2': Number of parameters
methodA()                        3': Number of parameters
methodA(double, int)             4': Order of parameters
methodA(int, double)             5': Same as 1'

The first four implementations of the method named methodA are overloaded correctly, each time with a different parameter list and, therefore, different signatures. The declaration at (5) has the same signature methodA(int, double) as the declaration at (1) and, therefore, is not a valid overloading of this method.

void bake(Cake k)  { /* ... */ }                 // (1)
void bake(Pizza p) { /* ... */ }                 // (2)

int     halfIt(int a) { return a/2; }            // (3)
double  halfIt(int a) { return a/2.0; }          // (4) Not OK. Same signature.

The method named bake is correctly overloaded at (1) and (2), with two different parameter lists. In the implementation, changing just the return type (as shown at (3) and (4) in the preceding example), is not enough to overload a method, and will be flagged as a compile-time error. The parameter list in the declarations must be different.

Only methods declared in the same class and those that are inherited by the class can be overloaded. Overloaded methods should be considered to be individual methods that just happen to have the same name. Methods with the same name are allowed, since methods are identified by their signature. At compile time, the right implementation of an overloaded method is chosen, based on the signature of the method call. Details of method overloading resolution can be found in §7.10 on page 316. Method overloading should not be confused with method overriding (§7.2, p. 268).

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020