Java 3 Odds Ends Advanced Programming Techniques javac options deprecation to get deprecation information d to specify the destination for class files verbose for more detailed output O for optimization java options Use D to specify properties Some often used properties http proxyHost http proxyPort Use X to specify non standard properties Xms size set initial Java heap size See java documentation for more info Security manager Djava security manager installs the default security manager very restrictive Djava security policy specifies the policy file Use policytool utility to generate policy files jar Use jar utility to create jar files Command format like tar File format like zip but includes a manifest file MANIFEST MF Jar files can be made executable by adding a Main Class line to the manifest javadoc javadoc utility generates an HTML documentation API with all the classes information Uses the code and the special javadoc comments starts the special doc comment ends it javadoc continued author author name for class param parameter name and description method return description of return value method exception exception name and description deprecated an item is obsolete and shouldn t be used class method or variable javadoc example package stars ui import java awt A Viewer for text author Thomas Funck version 1 0 see Viewer public class TextViewer extends Frame implements Viewer The TextArea used to display text private TextArea text Creates a new TextViewer public TextViewer Sets the object to be viewed param o the object to be viewed exception ClassCastException thrown when the specified object is not of type String public void setObject Object o throws ClassCastException Java threads Use the built in Thread class in Java You need to supply the programming that the thread will follow in order to do multithreaded programming There are two ways to get a new thread in Java Extend subclass the Thread class Provide a run method in the subclass Create a Thread object incorporating an object that specifies the Thread s run method extend subclass the built in Thread class In file AThread java class AThread extends Thread public AThread String name super name public void run System out println My name is getName In file test java class test public static void main String args AThread a new AThread mud Thread name a start implement Runnable interface In file AClass java class AClass implements Runnable public void run System out println My name is Thread currentThread getName In file test2 java class test public static void main String args AClass aObject new AClass Use alternative constructor for Thread class Thread aThread new Thread aObject mud too Thread name aThread start versus implement Runnable The implementing Runnable technique allows you to extend another class as well as getting threads Since Java does not have full multiple inheritance you can t do that with the first method Thread itself implements Runnable Thread Construction Different Thread constructors accept combinations of arguments supplying A Runnable object in which case Thread start invokes run of the supplied Runnable object A String that serves as an identifier Not useful except for tracing and debugging ThreadGroup in which the new Thread should be placed Starting threads Invoking its start method causes an instance of class Thread to initiate its run method A Thread terminates when its run method completes by either returning normally or throwing an unchecked exception Threads are not restartable even after they terminate isAlive returns true if a thread has been started by has not terminated More Thread methods Thread currentThread returns a reference to the current Thread Thread sleep long msecs causes the current thread to suspend for at least msecs milliseconds Thread interrupt is the preferred method for stopping a thread not Thread stop Priorities Each Thread has a priority between Thread MIN PRIORITY and Thread MAX PRIORITY from 1 to 10 Each new thread has the same priority as the thread that created it The initial thread associated with a main by default has priority Thread NORM PRIORITY 5 getPriority gets current Thread priority setPriority sets priority A scheduler is generally biased to prefer running threads with higher priorities depends on JVM implementation The run queue of runnable threads The Java language specification does not specify how Java is supposed to choose the thread to run if there are several runnable threads of equal priority One possibility pick a thread and run it until it completes or until it executes a method that causes it to move into a non running state Another possibility time slicing pick a thread and run it for a short period of time Then if it is not finished suspend it and pick another thread to run for the same period of time The semantics of yield public static void yield Causes the currently executing thread object to temporarily pause and allow other threads to execute Java Language Reference In some cases a large number of threads could be waiting on the currently running thread to finish executing before they can start executing To make the thread scheduler switch from the current running thread to allow others to execute call the yield method on the current thread In order for yield to work there must be at least one thread with an equal or higher priority than the current thread Thread synchronization t wait blocks until t notify or t notifyAll method is called Thread States and Scheduling A Java thread can be in new runnable running suspended blocked suspended blocked and dead The Threads class has methods that move the thread from one state to another Thread process states start yield stop 0 sleep suspend resume 1 2 run stop end 3 suspend dispatch stop stop 1 terminated 3 suspended 2 running 4 runnable 4 Thread states New state a Thread newly created Runnable after being started the Thread can be run It is put into the run queue of Threads and waits its turn to run Runnable does not mean running Running the thread is executing its code On a uniprocessor machine at most one thread can run at a time More thread states Blocked the thread is waiting for something to happen It is waiting for an i o operation it is executing to complete It has been told to sleep for a specified period of time through the sleep method It has executed the wait method and will block until another thread executes a notify or notifyAll method It will return to runnable state