CSC Java Programming, Fall, 2008 Week 2: Java Data Types, Control Constructs, and their C++ counterparts, September 4

References GNU make docs. has on-line docs. class lib. /export/home/faculty/parson/JavaLang on bill.kutztown.edu Make sure that /usr/jdk/jdk1.6.0_02/bin is near the front of UNIX PATH. Follow instructions in the JavaShellSetup.pdf document (accessible via my home page at to set up and verify your Java compilation environment.JavaShellSetup.pdfhttp://faculty.kutztown.edu/parson

First example Java program CountArgString counts distinct, non- overlapping occurrences of a string in a file /export/home/faculty/parson/JavaLang/week1/lecture1 Make sure you “cp –pr ~parson/JavaLang ~/JavaLang to get JavaLang into your home directory Make sure CLASSPATH include your $HOME/JavaLang makefile drives execution of compile and test steps gmake build to compile Java files gmake test to run test cases gmake clean to clean up test output and compiled files

Summary of Java built-in types Primitive type variables are not class objects byte is 8-bit signed, -128 through 127 (page 32 in text) short is 16-bit signed, through int is 32-bit signed, long is 64-bit signed float is 32-bit type and double is 64-bit type boolean is 1-bit true or false, char is UNICODE Some class types are built into the language java.lang.String a class built into the language Wrapper classes in java.lang wrap native types as classes. Examples are Integer, Float, Long, Double.

Summary of Java control constructs boolean (true or false) is the basis for control flow /export/home/faculty/parson/JavaLang/week1/bool for, while and do-while loops, just like C++ if.. else if.. else selection, just like C++ switch statement (text p. 86) also like C++ break exits the innermost loop or switch continue goes to the top of innermost loop There are no stand-alone functions! A method always exists inside a class. A non-static method uses a class object. A static method uses only class-static data.

Java Methods A method is equivalent to a C++ member function. In Java all methods resides in classes. A static method does not require an object. int intvar = java.lang.Integer.parseInt(“2”); System.out.println(“integer: “ + intvar); Statics method use static class variables. A regular method needs an object reference. Integer intObject = new Integer(“3”); System.out.println(“integer: “ + intObject.intValue());

Java storage of class and object data Only one copy of a static data element exists for its class. Both static methods and non- static methods (object methods) can use it. static java.lang.String oneStringPerClass = new String(); There is one copy of each non-static data element in each object. Only non-static methods can use it. String oneStringPerObject = new String(“my value”);

Java access to class and object methods and data Public methods and data can be used by any code that imports the class. Protected methods and data can be used only by the defining class and derived classes. Private methods and data can be used only by the defining class. If there is no explicit access restriction, then package methods and data can be used by any class in the package.

Boolean example code /export/home/faculty/parson/JavaLang/week1/bool Make sure you have a copy of this. cp –pr ~parson/JavaLang/week1/bool ~/JavaLang/week1/bool Program verifies valid command line args. 1. Program reads command line into an array of integers, raising an Exception if any of the command line arguments is not an integer. 2. Verify that array is in ascending order using &&. 3. Verify that array is in ascending order using ||.