Introduction to Java Programming Language May 2015 Kyung Eun Park COSC Introduction to Computer Science II

Contents 1.Primitive Data Types 2.Conditional (if) Statements 3.Loops 4.User Input/Output: Scanner and File classes 5.String 6.Arrays 7.Methods 8.Class as a Program 9.Class as an Object Class 10.Class as a Module Java key facts 2

1. Data Types Primitive data types and variable declarations – int int numb; int max = -1000; int min = 1000; int x, y, z; – double double average; double balance=0.0; – char char letter; char ch=‘q’; – boolean boolean isOdd; boolean isChar=true; 3

2. Conditional (if) Statements if/else if (num%2==0) System.out.println(num+” is even number”); else System.out.println(num+” is odd number”); if/else if/else if (grade>=90) { grade = ‘A’; } else if (grade>=80) { grade = ‘B’; } else { grade = ‘C’; } 4

3. Loops for loop for (int i=0; i<list.length; i++) { list[i]++; } while loop while (input.hasNext()) { name = input.next(); } do … while loop sum = 0; do { sum = sum + num % 10; num = num/10; } while (num>0); 5

4. User Input/Output (1) 6 File and Scanner import java.io.*; import java.util.*; … File file = new File(“mydata.txt"); Scanner input = new Scanner(file); or Scanner input = new Scanner(new File(“mydata.txt”)); Methods canRead(),delete(),exists(),getName(),length(),renameTo(file) Usage File f= new File(“example.txt”); if (f.exists() && f.length() > 1000) { f.delete(); } Exception Handling public static void main(String[] args) throws FileNotFoundException { Scanner input = new Scanner(new File(“data.txt”)); … }

4. User Input/Output (2) Scanner import java.util.*; … Scanner input = new Scanner(new File("data.txt")); if (input.hasNext()) { String name = input.next(); } Scanner line = new Scanner(string); Methods hasNext(), hasNextInt(), hasNextDouble(), hasNextLine() next(), nextInt(), nextDouble(), nextLine() 7

5. String 8 Variable declarations String first_name = “Kyung Eun”; String last_name = “Park”; String name = last_name + “, “ + first_name; Methods String s = “hello”; charAt(index) s.charAt(1) returns "e" contains(text) s.contains("hi") returns false endsWith(text) s.endsWith("llo") returns true equals(text) s.equals("hello") returns true equalsIgnoreCase(text) s.equalsIgnoreCase("Hello") returns true indexOf(text) s.indexOf("o") returns 4 length() s.length() returns 5 startsWith(text) s.startsWith("hi") returns false substring(start, stop) s.substring(1,3) returns "el" toLowerCase() s.toLowerCase() returns "hello" toUpperCase() s.toUpperCase() returns "HELLO" Useful conversion methods Integer.parseInt(numStr) returns int value, 324 converted from str like “324”. String numStr = “324”; int numInt = Integer.parseInt(numStr); // 324 double numDbl = Double.parseDouble(“ ”); //

6. Arrays 9 Syntax import java.util.*; … type[] name = new type[length]; type[] name = {value 1, value 2, …, value n }; Accessing array name[index] name[index] = value; name.length Methods binarySearch(), copyOf(), equals(), fill(), sort(), toString() Usage int days = 31; int[] temps = new int[days]; Arrays.sort(temps);

7. Methods Static method – Part of a class, rather than part of an object. – Not copied into each object; shared by all objects of that class. – No implicit parameter – Syntax public static type name ( parameters ) { statements ; } Instance method (or object method) – exists inside each object of a class and gives behavior to each object – has implicit parameter, this. – Syntax public type name ( parameters ) { statements ; } 10

8. Class as a Program Has a main and other static methods. Does not usually declare any static fields. (except final ) Works as a driver (test) of object class(es) Example: – GuessingGame, PointMain, BankMain, COSCDepartment, etc. 11

9. Class as an Object Class Defines a new type of objects. Declares object fields, constructor(s), and methods. Might declare static fields or methods, but these are less of a focus. Should be encapsulated Example: – Point, BankAccount, Date, Student, etc. 12

10. Class as a Module A module is a partial program, not a complete program. – no main() Used as utility code implemented as static methods Example: Math Syntax class. method ( parameters ); Usage int factorsOf24 = Factors.countFactors(24); 13