1. Data Types and Control Structures CS3250

2. Java Data Types Everything is an Object Except Primitive Data Types –For efficiency –Platform independent Portable “slow” Objects are often required –In collections, for example Every primitive has a corresponding object wrapper

3. Primitive Types PrimitiveSizeMinMaxWrapper boolean—— — Boolean char16UnicodeCharacter byte8-128127Byte short16-2 15 2 15 -1Short int32-2 31 2 31 -1Integer long64-2 63 2 63 -1Long float32IEEEFloat double64IEEEDouble void———Void All are signed except boolean and char

4. Java Character Type Internationalization –16-bit Unicode character. –ASCII is a subset of Unicode - ISO-8859 (Latin-1) –Escape sequence: \uhhhh: hex-decimal code, e.g. \u000A \ddd: octal code, e.g. \040 \n, \t, \b, \r, \f, \\, \', \". Java programs are also in Unicode. Unicode standard: http://www.unicode.org

5. Operators Much the same as C++ –Booleans are short circuit New operators: –instanceof –>>> logical right shift: fills in with zeros rather than sign bit Important difference –Binary operands are evaluated left-to-right: x = f() + g(); –Equality operator (==) only checks object references (use equals() instead)

6. Enumerated Types New in JDK 5.0 Has finite number of named values Cannot be local to a method Will print name, not number ( toString does the right thing) More info in Chapter 5 of textbook enum Day {FRIDAY, SATURDAY, SUNDAY}; Day today = Day.FRIDAY;

7. The String Class Strings are first-class objects. Strings are not arrays of char 's. String index starts from 0. String constant: "AStringConstant" String concatenation s1+s2 and s1+=s2 s.length() the length of a string s s.charAt(i) character at position i Strings are immutable.

8. Comparing Strings String s1 = "foo", s2 = "goo"; if (s1.equals(s2))... String s1 = "foo", s2 = "foo"; if (s1 == s2)... You should not use == to compare characters in two strings. –Will compile –Will give the expected results in some situations (with shared strings). –Will not give the expected results in other situations (e.g., result of substring method). Use the equals method instead:

9. Input Prior to JDK 5.0: –learn the magic formula or –get an input class from a textbook JDK 5.0 and beyond: –Use the Scanner class in the java.util package InputTest.java example from book (p. 64 8 th ed.) –Still some issues: nextLine() after nextInt() "subtle bugs" with more than one scanner on the same stream

10. File Input Scanner in = new Scanner(new File("myfile.txt")); String line = in.nextLine();

11. Output System.out.print System.out.println System.out.printf –Similar to the C function with the same name –New with JDK 5.0 –Not the only way to format output, but the easiest. int age = 42; System.out.printf("I am %d years old", age);

12. Formatting without Printing String hiStr = String.format("Hi %s", name);

13. File Output public PrintWriter openOutFile(String fileName) { PrintWriter out = null; try { out = new PrintWriter(fileName); } catch (IOException x) { x.printStackTrace(); } return out; } out.println("Hello, File");

14. Control Flow The same as C and C++ except: No goto labeled break and continue "for each" loop –new with JDK 5.0 –discussed with arrays

15. Constrained Branching Labeled break –To exit deeply nested loops –Example: Loop (from Prof. Allison's examples) Labeled continue –To cycle on outer loops –Example: Nested3 (from Prof. Allison's examples)

16. Non-standard Flow Errors alter the execution path of a program Error handling techniques should be simple Exceptions: –Provides an alternate return mechanism from functions –Should only be used in exceptional cases (that is, for errors) Continued in Exceptions.ppt

17. Arbitrary Precision Arithmetic Classes BigInteger and BigDecimal Arbitrarily long sequences of digits Use methods instead of operators for addition, subtraction, etc. Use static valueOf method to convert normal values to Big values: BigInteger a = BigInteger.valueOf(100); Example: BigIntegerTest.java, p. 89 (8 th ed)

18. int[] ia = new int[3]; int ia[] = new int[3]; int[] ia = {1, 2, 3}; float[][] mat = new float[4][4]; for (int y = 0; y < mat.length; y++) { for (int x = 0; x < mat[y].length; x++) mat[y][x] = 0.0; } Java Arrays Arrays are first-class objects. –sized at runtime! Indexes are always bounds-checked. Array index starts from 0.

19. The "for each" Loop New in JDK 5.0 loop through elements in an array or in a collection ( Vector, List, etc.) –elements must be in class that implements Iterable String[] names = {"Groucho", "Harpo", "Chico"}; for (String name : names) System.out.println(name);

20. More about Arrays… Copying: System.arraycopy(from, fromIndex, to, toIndex, count); Sorting: import java.util.*; int[] a = new int[10000]; … Arrays.sort(a);