Methods

1. Methods Creation Parameters Return values

2. Methods definition • Sometimes calledfunctions • Methods implements some operation of objects • Identifier begins with a small letter. If consists of more than one word everynext word starts with capital letter • Examples:setColor(), openWindow(), readData() • Methods definition belongs into class declaration • It is not possible to put one method into another

3. Methods definition Method’s head modifiertypeidentifier(formal_parametrs) { local_variables; statements; return ret_value; } • Modifier defines access level – public, private, protected (see later) • Typespecifies the type of the return value • Parameters specifies type and identifier of input values body If type is other then void

4. Methods • Executes algorithm of some operation • Works with class attributes and parameters input values (data) • Can return a value output data

5. Access methods • Selectors • Do not modify values only get access to particular attributes in so called read-only mode • The value can be computed based on the values of class attributes • They are called get methods - getColor() • Modifiers • Change the values of attributes • Transforms input data (parameters) into values of attributes • They are called set methods - setColor(value)

6. Methods without return value public voiddrawSomething() { graph.drawRect(10,10,200,110); } Methods with parameters public void kresliObdelnik(int sirka,int vyska) { graph.drawRect (10,10,sirka,vyska); }

7. Methods with return value public int maximum(int a, int b) { return (a>b)? a : b; } • If the there is a given type in the method’s head (i.e. type is other thenvoid), there has to be also return in the body of the method • returndiscontinues the execution of the method

8. Calling (using) methods • Call statement If methods returns a value: variable = method_identifier(actual_parameters); If not: method_identifier(actual_parameters); • Calling methods of other objects object_identifier.method_identifier();

9. Calling methods (example) int a = 10, c; c = maximum (a,200); drawRectangle(230,222); drawCircle(100,maximum(a,200)); out.print(“Hello”);

10. Actual and formal parameters • Formal parameters • Only in the methods definition • Becomes local variable • Value is given by copying from an actual parameter • Actual parameters • When calling a method • Data (constants, attributes, variables), that are transferred into methods • Are copied into formal params

11. Actual and formal parameters • Params of primitive data types(int, float, char, also String ...) • Changes to the formal parameter inside a method doesn’t effect actual parameters • Params of reference data types (arrays, instances, interfaces) • Changes to the formal parameter inside a method does effect actual parameters