m1.w4.d2 - parameters

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m1.w4.d2 - parameters

  1. 1. Methods with parameters Monday, September 9, 13
  2. 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. 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. 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. 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. 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 Monday, September 9, 13
  7. 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 Monday, September 9, 13
  8. 8. 8 Lab! • See https://dl.dropboxusercontent.com/u/20418505/Labs/ M1.W4-1.txt Monday, September 9, 13

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