The document discusses how to define methods that take parameters in Java. It shows examples of a printSquares method that initially prints the squares of numbers from 1 to 5 hardcoded. It is then modified to take an int parameter called maxSquare so that it can print squares up to any given number by passing different values for maxSquare. This allows the behavior of the method to be customized each time it is called rather than being hardcoded. The document also discusses formal parameters in a method definition versus actual parameters passed during a method call.

1. Methods with parameters
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2. 2
Parameters
• The method below will print the first 5 squares:
public class ParameterTest {
public static void printSquares() {
for (int i = 1; i <= 5; i++) {
System.out.println(i + " squared = " + i * i);
}
}
public static void main(String[] args) {
printSquares();
}
}
• What if we wanted to make this print an arbitrary number of
squares?
Monday, September 9, 13

3. 3
Parameters
• You could assign try to assign a variable to do it:
public class ParameterTest {
public static void printSquares() {
for (int i = 1; i <= maxSquare; i++) {
System.out.println(i + " squared = " + i * i);
}
}
public static void main(String[] args) {
int maxSquare = 5;
printSquares();
}
}
// won’t work!
Monday, September 9, 13

4. 4
Parameters
• Instead, we can have printSquares() take a parameter:
public class ParameterTest {
// maxSquare is a variable local to the method
public static void printSquares(int maxSquare) {
for (int i = 1; i <= maxSquare; i++) {
System.out.println(i + " squared = " + i * i);
}
}
public static void main(String[] args) {
printSquares(5);
}
}
• formal parameter (variable) vs. actual parameter (value)
Monday, September 9, 13

5. 5
Parameters
• The actual parameters passed to a method call can be
expressions:
public class ParameterTest {
public static void printSquares(int maxSquare) {
for (int i = 1; i <= maxSquare; i++) {
System.out.println(i + " squared = " + i * i);
}
}
public static void main(String[] args) {
int firstMax = 5, secondMax = 8;
printSquares(firstMax); // prints all squares to 5
printSquares(secondMax + 1); // prints all squares to 9
}
}
Monday, September 9, 13

6. 6
Scoping methods
public class ParameterTest {
public static void printSquares(int maxSquare) {
for (int i = 1; i <= maxSquare; i++) {
System.out.println(i + " squared = " + i * i);
}
}
public static void main(String[] args) {
int firstMax = 5, secondMax = 8;
printSquares(firstMax); // prints all squares to 5
printSquares(secondMax + 1); // prints all squares to 9
}
}
method main method printSquares method printSquares
firstMax
secondMax
maxSquare maxSquare5
8
5 9
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7. 7
Scoping methods
• Be careful with the way you name parameters:
public class ParameterExample {
public static void main(String[] args) {
int x = 4;
doubleNumber(x);
System.out.println("x = " + x);
}
public static void doubleNumber(int x) {
System.out.println("Initial value = " + x);
x *= 2;
System.out.println("Final value = " + x);
}
}
method main method doubleNumber
x x4 48
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8. 8
Lab!
• See https://dl.dropboxusercontent.com/u/20418505/Labs/
M1.W4-1.txt
Monday, September 9, 13