Introduction to methods

1. Chapter 5-4: Classes and Objects in Depth Introduction to methods

2. Method Overloading: An Introduction Method overloading: more than one method can have the same name Two methods are said to have different formal parameter lists if both methods have: A different number of formal parameters, or If the number of formal parameters is the same, then the data type of the formal parameters, in the order you list, must differ in at least one position Java Programming: From Problem Analysis to Program Design, 4e

3. Method Overloading public void methodOne(int x) public void methodTwo(int x, double y) public void methodThree(double y, int x) public int methodFour(char ch, int x, double y) public int methodFive(char ch, int x, String name) These methods all have different formal parameter lists Java Programming: From Problem Analysis to Program Design, 4e

4. Method Overloading (continued) public void methodSix(int x, double y, char ch) public void methodSeven(int one, double u, char firstCh) The methods methodSix and methodSeven both have three formal parameters and the data type of the corresponding parameters is the same These methods all have the same formal parameter lists Java Programming: From Problem Analysis to Program Design, 4e

5. Method Overloading (continued) Method overloading: creating several methods, within a class, with the same name The signature of a method consists of the method name and its formal parameter list Two methods have different signatures if they have either different names or different formal parameter lists Note that the signature of a method does not include the return type of the method Java Programming: From Problem Analysis to Program Design, 4e

6. Method Overloading (continued) The following method headings correctly overload the method methodXYZ: public void methodXYZ() public void methodXYZ(int x, double y) public void methodXYZ(double one, int y) public void methodXYZ(int x, double y, char ch) Java Programming: From Problem Analysis to Program Design, 4e

7. Method Overloading (continued) public void methodABC(int x, double y) public int methodABC(int x, double y) Both these method headings have the same name and same formal parameter list These method headings to overload the method methodABC are incorrect In this case, the compiler will generate a syntax error Notice that the return types of these method headings are different Java Programming: From Problem Analysis to Program Design, 4e

8. Scope of an Identifier within a Class Local identifier: identifier declared within a method or block, which is visible only within that method or block Java does not allow the nesting of methods; you cannot include the definition of one method in the body of another method Within a method or a block, an identifier must be declared before it can be used; a block is a set of statements enclosed within braces Java Programming: From Problem Analysis to Program Design, 4e

9. Scope of an Identifier within a Class (continued) • A method’s definition can contain several blocks • The body of a loop or an if statement also form a block • Within a class, outside of every method definition (and every block), an identifier can be declared anywhere Java Programming: From Problem Analysis to Program Design, 4e

10. Scope of an Identifier within a Class (continued) Within a method, an identifier used to name a variable in the outer block of the method cannot be used to name any other variable in an inner block of the method For example, in the method definition on the next slide, the second declaration of the variable x is illegal Java Programming: From Problem Analysis to Program Design, 4e

11. Scope of an Identifier within a Class (continued) public static void illegalIdentifierDeclaration() { int x; //block { double x; //illegal declaration, //x is already declared ... } } Java Programming: From Problem Analysis to Program Design, 4e

12. Scope Rules Scope rules of an identifier declared within a class and accessed within a method (block) of the class An identifier, say X, declared within a method (block) is accessible: Only within the block from the point at which it is declared until the end of the block By those blocks that are nested within that block Java Programming: From Problem Analysis to Program Design, 4e

13. Scope Rules (continued) • Suppose X is an identifier declared within a class and outside of every method’s definition (block) • If X is declared without the reserved word static (such as a named constant or a method name), then it cannot be accessed in a static method • If X is declared with the reserved word static (such as a named constant or a method name), then it can be accessed within a method (block), provided the method (block) does not have any other identifier named X Java Programming: From Problem Analysis to Program Design, 4e

14. Example 7-11 public classScopeRules { static final double rate = 10.50; static int z; static double t; public static void main(String[]args) { intnum; doublex, z; charch; //... } public static void one(int x, char y) { //... } Scope Rules (continued) public static int w; public static void two(int one,int z) { charch; int a; //block three { int x = 12; //... } //end block three //... } } Java Programming: From Problem Analysis to Program Design, 4e

15. Scope Rules: Demonstrated Java Programming: From Problem Analysis to Program Design, 4e

16. Scope Rules: Demonstrated (continued) Java Programming: From Problem Analysis to Program Design, 4e