1. Lecture 11
Parameters
CSE 1322
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2. What is a Method?
Think of a method as a black box that contains the detailed implementation for a specific task. The method may use inputs (parameters) and may return an output with a specific type.
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3. Method Structure
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4. Method Structure
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5. Parameters and Argument Passing
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6. Parameters There are three main types of parameters:
Value - passes a copy (value) of the variable to the method.  This is the default.
Reference (C#)- passes a reference to the actual variable.  Marked with "ref", use this when you want to pass a value in and have any change to that value be persistent when the method is complete
Out (C#) - passes a reference to the actual variable.  Marked with "out", use this when you want the method to generate a value and place it for later use in the actual variable (persists when the method is complete)
Note that java passes all parameters by value.
C++ uses both Call-by-reference and Call-by-value
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7. Example 1 and the output is ?
static void Main(String[] args) { int a = 42; Console.WriteLine (a); // Prints 42 B (a); // Prints 51 // Call-by-value; Console.WriteLine (a); // Prints 42 } static void B (int x) // Built-in type argument passing x += 9; Console.WriteLine (x);
A Call-by-value Method with C#
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8. Example 1 and the output is ?
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9. Example 1 and the output is ?
static void Main(String[] args) { int a = 42; System.out.println (a); // 42 B (a); // 51 System.out.println (a); // 42 } static void B (int x) x += 9; System.out.println (x);
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10. A Call-By-Value Example with Java
public class CallByValueEx2 {
public static void main(String[] args) {
String myname = "Mokter";
// myname is a is String reference local variable
System.out.println("Initially, inside main(), Name = " + myname );
callMe(myname);
System.out.println("After calling callMe(), Name = " + myname);
// Look here ??!!??
System.out.println("Now, inside main(), Name = " + myname ); }
static void callMe(String newname ) {
// newname is String reference argument
newname = "Dr. Mokter Hossain";
System.out.println("Inside callMe(), Name = " + newname );
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11. A Call-By-Value Example with Java
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12. Example 2 and the output is ?
static void Main(String[] args ) { int a = 42; Console.WriteLine (a); B (ref a); } static void B (ref int x) x += 9; Console.WriteLine (x);
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13. Example 2 and the output is ?
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14. Example 42 and the output is ?
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15. Example 3 and the output is ?
The out works same as ref but it is optional to initialize in the caller method
Example 3 and the output is ?
static void Main(String[] args) { int a; // NOT initialized B (out a); Console.WriteLine (a); } static void B (out int x) { x = 9; Console.WriteLine (x);
Source:
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16. Example 3 and the output is ?
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17. Example 4 and the output is ?
using System; namespace CSE1322ReviewCS{ class Program { class Z { public int y; } static void Main(String[] args) { Z myZ = new Z(); myZ.y = 42; Console.WriteLine(myZ.y); B(myZ); Console.WriteLine("Press any key to exit."); Console.ReadKey(); } static void B(Z x) { x.y += 9; Console.WriteLine(x.y);
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18. Example 4 and the output is ?
class Z { public int y; } static void Main() { Z myZ = new Z(); myZ.y = 42; System.out.println (myZ.y); B (myZ); } static void B (Z x) x.y += 9; System.out.println (x.y);
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19. Example 4 and the output is ?
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20. Example 5 and the output is ?
using System; class Example5 { class Z { public int y; } static void Main(String[] args) { Console.WriteLine("Example5...."); Z myZ = new Z(); myZ.y = 42; Console.WriteLine(myZ.y); B(ref myZ); Console.ReadKey(); } static void B(ref Z x) { x = new Z(); x.y = 1; Console.WriteLine(x.y);
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21. Example 5 and the output is ?
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22. Pass-by-value vs. Pass-by-reference vs. Pass-by-reference-type
Be careful to note the difference between a pass-by-reference parameter and a parameter of a reference type.
Use the activation stack to track local variables and how parameters of the above types affect the variables from one stack frame to the next.
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23. Overloading Methods
Method overloading is the process of using the same method name for multiple methods
The signature of each overloaded method must be unique
The signature includes the number, type, and order of the parameters
The compiler determines which version of the method is being invoked by analyzing the parameters
The return type of the method is not part of the signature
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24. Overloading Methods float tryMe (int x) { return x + .375; } Version 1
float tryMe (int x, float y) {
return x*y; }
Version 2
result = tryMe (25, 4.32f)
Invocation
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25. Overloading Operators
In C#, not only can methods be overloaded, operators can be overloaded as well.
Java does not allow operator overloading
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27. Operator overloading
C# enables you to overload most operators to make them sensitive to the context in which they are used.
Use operator overloading when it makes an application clearer than accomplishing the same operations with explicit method calls.
Class ComplexNumber overloads the plus (+), minus (-) and multiplication (*) operators to enable programs to add, subtract and multiply instances of class ComplexNumber using common mathematical notation
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28. Operator Overloading
Keyword operator, followed by an operator symbol, indicates that a method overloads the specified operator.
Methods that overload binary operators must take two arguments—the first argument is the left operand, and the second argument is the right operand.
Overloaded operator methods must be public and static.
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30. Overload the plus operator (+) to perform addition of ComplexNumbers
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