Lesson 8: Methods
Recall that in Visual Basic you put your code inside “subs.” For example, if you wanted code to execute
when a button was clicked, you put it inside a button’s click sub, as shown:
Private Sub Button1_Click(ByVal sender As System.Object,…
MsgBox("Hi")
End Sub
Recall further that when you had repeated code, you saved time by writing your own subs, then calling
those subs from other subs. For example, clicking any of three buttons causes the checkForEnd sub
in the VB example below to execute.
Public Class Form1
Dim money As Integer = 0
Private Sub Button1_Click(ByVal sender As Object, ByVal e…
money = money + 1
checkForEnd()
End Sub
Private Sub Button2_Click(ByVal sender As Object, ByVal e…
money = money + 2
checkForEnd()
End Sub
VB
Private Sub Button3_Click(ByVal sender As Object, ByVal e…
money = money + 3
checkForEnd()
End Sub
Private Sub checkForEnd()
Label1.Text = "$" & money
If money > 10 Then
MsgBox("You have more than $10.
Me.Close()
End If
End Sub
End Class
You’re rich!
Bye.")
Java calls subs methods. So far, you have put all your code into a method named main. Now you will
learn how to write three varieties of your own methods: methods without parameters (easiest),
methods with parameters (medium difficulty), and methods with return values (hardest, most
important, and optional in my VB course). The last category will get its own packet.
Methods without Parameters
Here is a simple java method:
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1
3
2
printStuff()
public static void
{
System.out.println("stuff");
System.out.println("more stuff");
System.out.println("even more stuff");
}
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1. Prepare to be annoyed. Ready? Good. Because you are not ready to understand these java
keywords yet. Just write them when you create a method. We will learn about them later.
2. The method’s name. Notice that the first letter of a method name should be lowercase, but the
first letter of any following words should be upper case. Follow this convention (it’s the same
convention used for variable names). It makes life easier later.
3. The whole top line – keywords, name and parameters (the contents of the parentheses – none,
yet) together – form the method’s signature.
4. The method’s contents are contained by braces.
We call the new method from the main method as shown:
public class MethodExample {
public static void printStuff() {
System.out.println("stuff");
System.out.println("more stuff");
System.out.println("even more stuff");
}
public static void main (String [] args) {
printStuff();
printStuff();
}
}
The above code causes the printStuff method to execute twice, so six lines of output appear on the
console. Note that the order in which you write the methods is not important. Java always starts
execution with main. However, traditionally main is the last method in the class.
Methods with Parameters
Often methods require information in order to do their jobs. For example, if a method displays the sum
of two ints, it must be told what specific values to add. A piece of information required by a method is
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called a parameter. Method parameters are defined inside of parentheses after the method name, as in
this example:
1. Parameters
public static void add(int a, int b) {
int result = a + b;
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System.out.println(a + " + " + b + " = " + result);
}
1. Look back at the first java method example (printStuff). Notice that there are empty
parentheses at the end of the signature (first line). That is because printStuff does not need
any information in order to do its job: it always prints the same thing. Add, however, needs to
know what numbers should be added, so it has two parameters, a and b, declared inside
parentheses at the end of the signature. Each parameter is declared with a type and a variable
name. The parameters are separated by commas.
2. Declare temporary variables inside methods as needed.
Here is a program that uses the add method several times:
public class MethodExample2 {
public static void main (String [] args) {
add(3, 5);
int x = 18;
int y = 21;
add(x, y);
double z = 1.932;
add(x, (int) z);
}
public static void add(int a, int b) {
int result = a + b;
System.out.println(a + " + " + b + " = " + result);
}
}
To call a method with parameters, write the method name, then parentheses, then values to match the
required parameters. In the example, each of the three calls to add was followed by parentheses
containing the two integers to add. Note that z had to be cast as an int in order to meet the
requirements of the second add parameter.
Parentheses
In java, you know when code is calling a method because the method name MUST be followed by a set
of parentheses.
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Math.random();
NOT
Math.random;
In VB, parenthes were optional. In java, you must follow the method name with parentheses, even if
they are empty (have no arguments). 1
ASSIGNMENTS
DelayCarpal
description:
1. Write a method that takes one String (that is, one String parameter) and one integer (one
integer parameter).
2. The method displays the String the number of times indicated by the integer. Call the method
three times from main with various strings and numbers.
3. Make sure your output is patterned according to the example output, below.
Example Console Output
Argula
Argula
Argula
Argula
cent
cent
cent
Utah
Utah
Utah
VoidTester
description:
1. Write a method that has three parameters, all integers.
2. Inside the method, test to see whether the last integer parameter is between the first two
integers, NOT inclusive.
3. Display the result of the test from within the method. See the example output, below.
4. Call the method 50 times from main, each time with three newly randomly generated integers.
In each set, the lower number should be from 1 to 20, inclusive, the upper number should be
from 81 to 100, inclusive, and the number to be checked should be from 1 to 100, inclusive.
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The presence or absence of parentheses is how java tells the difference between a method and a variable.
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Example Console Output
10 is between 2 and 97
31 is between 6 and 87
31 is between 4 and 89
63 is between 12 and 88
64 is between 13 and 100
9 is not between 17 and 99
58 is between 8 and 88
79 is between 6 and 90
20 is between 7 and 81
<<<<<41 more lines like this>>>>>
***Bonus Skill*** (needed for last assignment)
System.out.print(String) does almost exactly the same thing as its lookalike,
System.out.println(String). The difference: new new version (the one missing “ln”) does
not advance the cursor to a new line. Here is an example with code and the output it produces:
System.out.print(“*”);
System.out.print(“*”);
System.out.print(“*”);
System.out.println(“”);
System.out.println(“Chicken for lunch!”);
Console Output
***
Chicken for lunch!
BoxMaker
description: Write a method that takes an int parameter and uses it as the dimension (width and
height) for displaying a “box” of a single character. For example, if the parameter’s value is 5, the
method would display:
*****
*****
*****
*****
*****
Call the method three times from main, once with a value of 2, once with a value of 5 and once with a
value of 10. You should get the same output shown below.
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Example Console Output
**
**
*****
*****
*****
*****
*****
**********
**********
**********
**********
**********
**********
**********
**********
**********
**********
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