3. Essential Java Classes 5. Some Useful Classes презентация

3. Essential Java Classes 5. Some Useful Classes

Class System (1 of 2) contains several useful class fields and methods it cannot be instantiated standard input, standard output, and error output streams gets and sets system properties

Class System (2 of 2) exit(int status) - terminates the currently running Java Virtual Machine gc() - runs the garbage collector arraycopy(…) - copies an array console() - Returns the unique Console object associated with the current JVM nanoTime() - Returns the current value of the running JVM high-resolution time See http://docs.oracle.com/javase/7/docs/api/java/lang/System.html for details

Class Runtime Allows to interface with the environment in which the application is running static getRuntime() - Returns the runtime object associated with the current Java application freeMemory() - returns the amount of free memory in the JVM totalMemory() - returns the total amount of memory in the JVM.

Example of String Command Execution Runtime r = Runtime.getRuntime(); try{ r.exec("C:\\Program Files\\Mozilla Firefox\\firefox.exe"); } catch(Exception ex){ System.out.println(ex.getMessage()); }

Class Properties represents a persistent set of properties as pairs of key-value details are here: http://docs.oracle.com/javase/tutorial/essential/environment/properties.html http://docs.oracle.com/javase/7/docs/api/java/util/Properties.html

Configuration File Example dbpassword=pass&word database=localhost dbuser=vmo

Use Properties Example Properties applicationProps = new Properties(); in = new FileInputStream("appProperties"); applicationProps.load(in); in.close(); String dbInfo = applicationProps. getProperty("database");

Class Object (1 of 2) The root of the class hierarchy Every class has Object as a superclass All objects, including arrays, implement the methods of this class See http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html for details

Class Object (2 of 2) equals(Object obj) - indicates whether some other object is "equal to" this one getClass() - returns the runtime class of this Object clone() - creates and returns a copy of this object toString() - returns a string representation of the object

Class Random is used to generate a stream of pseudorandom numbers Random(long seed) - creates a new random number generator nextInt() - returns the next pseudorandom, uniformly distributed int value nextInt(int n) - returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive) See http://docs.oracle.com/javase/7/docs/api/java/util/Random.html for details

Class Math (1 of 2) Contains methods for performing basic numeric operations: elementary exponential, logarithm, square root trigonometric functions See http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html for details

Class Math (2 of 2) sqtr(double value) exp(double value) log(double value) power(double value, double p) sin(double value) sinh(double value) toRadians(double value)