Consider the cards one at a time and insert each into its proper place among those already considered keeping them sorted. The following code mimics this process in a Java method that sorts strings in an array: Here is an example when i is 6: This process es executed first with i equal to 1 , then 2 , then 3 , and so forth, as illustrated in the following trace. The inner loop of the insertion sort code is within a double nested for loop, which suggests that the running time is quadratic, but we cannot immediately draw this conclusion because of the break. Sorting other types of data.
We want to be able to sort all types of data, not just strings. For sorting objects in an array, we need only assume that we can compare two elements to see whether the first is bigger than, smaller than, or equal to the second. Java provides the Comparable interface for this purpose. To develop a faster sorting method, we use a divide-and-conquer approach to algorithm design that every programmer needs to understand.
Insertion sort.
To mergesort an array, we divide it into two halves, sort the two halves independently, and then merge the results to sort the full array. To sort a[lo, hi , we use the following recursive strategy: If the subarray length is 0 or 1, it is already sorted. Here is a trace of the contents of the array during a merge. See the book for for details. The difference between n 2 and n lg n makes a huge difference in practical applications. The same basic approach is effective for many important problems, as you will learn if you take a course on algorithm design.
A problem A reduces to a problem B if we can use a solution to B to solve A. For example, consider the problem of determining whether the elements in an array are all different. This problem reduces to sorting because we can sort the array, the make a linear pass through the sorted array to check whether any entry is equal to the next if not, the elements are all different. We accomplish this by two sorts. Our first step is to sort the strings on standard input. In this case, we are not so much interested in the fact that the strings are put into sorted order, but in the fact that sorting brings equal strings together.
If the input is to be or not to be to then the result of the sort is be be not or to to to with equal strings like the three occurrences of to brought together in the array. Now, with equal strings all together in the array, we can make a single pass through the array to compute all the frequencies. Next, we sort the Counter objects. We can do so in client code without any special arrangements because Counter implements the Comparable interface.
The application highlighted in FrequencyCount. Exercises Write a filter Dedup. Creative Exercises This list of exercises is intended to give you experience in developing fast solutions to typical problems. Think about using binary search, mergesort, or devising your own divide-and-conquer algorithm. Implement and test your algorithm. Write a linear-time filter IntegerSort.
For example, presented with the input sequence 98 2 3 1 0 0 0 3 98 98 2 2 2 0 0 0 2 your program should print the output sequence 0 0 0 0 0 0 1 2 2 2 2 2 3 3 98 98 98 Three sum. Given an array of n integers, design an algorithm to determine whether any three of them sum to 0. The order of growth of the running time of your program should be n 2 log n. Develop a program that solves the problem in quadratic time. Write a recursive program Quick. First, pick a random element v as the partitioning element. Next, partition the array into a left subarray containing all elements less than v, followed by a middle subarray containing all elements equal to v, followed by a right subarray containing all elements greater than v.
Finally, recursively sort the left and right subarrays. Write a program to read in a list of domain names from standard input, and print the reverse domain names in sorted order. For example, the reverse domain of cs. This computation is useful for web log analysis. To do so, create a data type Domain. Local minimum in an array. Given an array a[] of n real numbers, design a logarithmic-time algorithm to find a local minimum an index i such that both a[i-1] and a[i].
Web Exercises Union of intervals. Given N intervals on the real line, determine the length of their union in O N log N time. For example the union of the four intervals [1, 3], [2, 4. Suppose you have a coffee can which contains an unknown number of black beans and an unknown number of white beans.
Repeat the following process until exactly one bean remains: Select two beans from the can at random. If they are both the same color, throw them both out, but insert another black bean.
- Sorting and Searching.
- Regression test selection for Java software.
- 4.2 Sorting and Searching.
- Object-oriented Programming (OOP) Basics.
If they are different colors, throw the black one away, but return the white one. Prove that this process terminates with exactly one bean left.
Compiling and Optimizing Java 8 Programs for GPU Execution
What can you deduce about the color of the last bean as a function of the initial number of black and white beans? To initiate an illegal spam campaign, you have a list of email addresses from various domains the part of the email address that follows the symbol. To better forge the return addresses, you want to send the email from another user at the same domain. For example, you might want to forge an email from nobody princeton. How would you process the email list to make this an efficient task? Given an array of N elements, not necessarily in ascending order, devised an algorithm to find the kth largest one.
It should run in O N time on random inputs. Given two permutations, Kendall's tau distance is the number of pairs out of position. Useful in top-k lists, social choice and voting theory, comparing genes using expression profiles, and ranking search engine results. Given N points on a circle, centered at the origin, design an algorithm that determines whether there are two points that are antipodal , i. Your algorithm should run in time proportional to N log N. Repeat the previous question, but assume the points are given in clockwise order. Your algorithm should run in time proportional to N.
Given an array a[] of N distinct integers positive or negative in ascending order. There are N circuit elements in the plane. Generating code which assumes a certain set of sub-objects is likely to require recoding several times during the life span of a product. Automatic testing of object-oriented Internet applications also requires that certain obstacles be overcome.
A significant portion of testing of object-oriented product involves ensuring that the correct data values are assigned to the specific properties on these objects. In cases where the objects and their properties are structured around an evolving format of external data, as described above, test cases for objects must reflect external data format changes just as the objects and their properties must change. As with the labor required to manually write and maintain object constructors, the work required to manually maintain test cases for such objects as they evolve is also considerable. Additionally, to perform unit test and some functional verification testing, appropriate test data must be generated for each property on an object within an object-oriented application under development.
As with objects and their properties and test cases for the objects, test data for the object must evolve in conjunction with changes in the external data format around which the objects and properties are structured. Independent or test came and test data generation, to instantiate an object for testing, object constructors typically require several arguments which dictate how the object is constructed. Often these values are calculated at the time the constructor is invoked.
Therefore, it may be difficult to determine the precise values passed on the constructor call for ascertaining how the object was to be constructed. An additional obstacle to automatic testing of object-orient applications is that, for full function of the product, real data must be accessed. Typically, however, accessing real data requires many different components of the final product to be functioning, which may be difficult during early development when components are often not completed.
Even in later development phases, the probabilities of problems downstream are increased in proportion to the number of components which need to be accessed. Complex nested data structures may also impede automatic code generation and testing in object-oriented applications. The nesting is required due to utilization of non-unique names for fields inside the nested structures.
Where nesting adds a significant level of complexity impeding automatic code generation and testing, the non-unique naming of data items poses a problem to flattening the data. It would be desirable, therefore, to provide mechanisms overcoming the problems described above and enabling automatic code generation and testing for object-oriented applications. It is therefore one object of the present invention to provide methods facilitating automatic coding of object-oriented applications.
It is another object of the present invention to provide methods facilitating automatic testing of object-oriented applications. It is yet another object of the present invention to provide a method for flattening complex data structures in object-oriented applications. The foregoing objects are achieved as is now described. To facilitate automatic code generation for Java and Javascript applications executed over the Internet, complex nested data structures resulting from non-unique naming of data fields are flattened.
Fully-qualified names for each data field are created. The fully-qualified names includes the names of all nodes within a nesting path for a given data field. Where fully-qualified names become overly cumbersome, aliases may be utilized and mapped to the fully-qualified names within a correlation table.
The object hierarchy for an application is thus simplified. The above as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description. The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:.
With reference now to the figures, and in particular with reference to FIG.
The exemplary embodiment depicted includes a client connected via communications link to the Internet Communications link may, for example, be in the form of access provided directly by an Internet service provider ISP or indirectly via a proxy within a firewall, as is known in the art. Client includes a Java-enabled browser application, allowing client to retrieve and display information formatted in accordance with the HyperText Markup Language HTML and to run Java applets, or a Java interpreter, allowing client to execute Java applications.
Also connected to Internet , via communications link , is server Java applets thus executed may be object-oriented applications formulated utilizing processes facilitating automatic coding and automatic testing and optimization of data structures in accordance with the present invention. Data processing system may be client or server depicted in FIG. Processor is connected to a level two L2 cache , which is utilized to stage data to and from processor at reduced access latency.
L2 cache is connected in turn to an interconnect or system bus , which is also connected, in the embodiment depicted, to system memory and memory-mapped graphics adapter Graphics adapter provides a connection for a display device not shown on which the user interface of software executed within data processing system is displayed. Pointing device may be a mouse, trackball, or the like. Those skilled in the art will appreciate that other devices may be incorporated into data processing system , such as an optical disk drive or a modem.
The operation of data processing systems of the type depicted in FIG. Processor executes the instructions within such program information and generates text or graphical information for presentation on display device connected via graphics adapter , where the information may be viewed by a user.
The user may selectively control operation of data processing system through input entered on keyboard or through pointing device In the present invention, the software implements the structures and methods described below for automatic generation and testing of Java or JavaScript object code.
With reference now to FIG. Data structures contain data around which an application or applet may be structured, and may comprise financial information residing on a server, such as server depicted in FIG. Data structure analysis module may be utilized to analyze data structures and generate a dictionary of data elements or provide other information to other modules.
Dictionary may be employed by an object generator attempting to automatically generate objects forming a Java or JavaScript application or applet. Lookup engine looks up a desired data element within dictionary and returns a pointer to the data element. This information may be used by object generator as described below. It is important to note that, although depicted as a single diagram, those skilled in the art will recognize that the structure depicted may actually be implemented within different data processing systems. For example, data structures , data analysis engine , dictionary , and lookup engine may all reside on one data processing system, such as a server for a financial institution.
The remainder of the modules depicted may reside on a client used to develop Java or JavaScript applications or applets. Pointer may be employed by object generator to create object constructors and , test data and real data versions, respectively. An input file containing a designation of which properties are to be implemented as sub-objects rather than properties on an object may also be employed by object generator , as may a rule base containing rules for naming properties on an object. Data structure analysis engine may also be utilized by test generator to create HTML page test cases for the object implemented by object generator , and to create test data structures for test data versions of automatically generated object constructors Lookup engine may also employ a correlation table created by object generator in instantiating objects from object constructors or The operation of the components depicted in FIG.
These processes may be implemented within the modules depicted in FIG. In accordance with the present invention, a dictionary of information related to offsets, links, etc. In the flowchart of FIG. The process illustrated may be utilized to create a dictionary for the first time, or to update an existing dictionary.
The process begins at step , which depicts starting analysis of the data structures utilized by an object-oriented application. The process then passes to step , which illustrates the optional step of verifying existing dictionary entries, if any. Such verification may be performed either by utilizing the dictionary entry to retrieve a corresponding data element, or by repeating the steps described below for the dictionary element.
This analysis may be performed, for example, by reading and analyzing the C header files which define the data structures. From such header files, the path of offsets and pointers required to retrieve each element within a given data structure may be determined. The process then passes to step , which illustrates updating the dictionary entries for data structure elements analyzed.
When created, the dictionary serves as a roadmap to each data structure element for a particular application. The process then passes to step , which depicts the process becoming idle until a subsequent dictionary creation or update is initiated. As an example of how this process may be employed, suppose a client-side Java object needs access to a complex data structure written, for instance, in C prior to the existence of Java. In C, data structures may contain fields and pointers to other data structures, which may in turn contain fields and pointers to other data structures, which may also contain fields and pointers to other data structures, etc An example might be the user profile information for a bank customer.
The top structure may have a few fields identifying the user, but may also contain a pointer to a structures containing all of the user demographic information. This demographic structure may also contain a pointer to an array of structures, one for each account which the user has at the bank.
Off of one of these specific structures may be an array containing the passwords for all cosigners required for any transaction on the account. A Java applet programmer may desire only to retrieve the first cosigner's password from the third checking account for a specific user. While it would not be particularly difficult to manually implement code for retrieving this field, this field may be one of thousands in the overall data definition. Handcrafting a single piece of code is not especially troublesome, but handcrafting thousands of pieces of code may become extremely burdensome.
Additionally, as new releases of the target data structure are created, architects of the data definition may decide to add or remove intermediate structures in the profile. Every handcrafted line of code may have to change in that situation. For Internet-based transactions, the problem is further complicated by the need, in order to access the data using standard handcrafted code, to transmit the entire data structure over the Internet to the client Java object to access the desired fields.
Availability of bandwidth may thus significantly impede the application. In the present invention, the complete data definition structures, fields, etc. This is a reasonable and generally accurate assumption given that header files are required for normal handcrafting of code. The path to every field in the entire data definition may therefore be enumerated in a dictionary, and assigned a unique numeric identifier. For example, the cosigner password field described above may be designated element The dictionary contains information for element such as:.
If the data structure changes from release to release, adding or removing intermediate structures, the dictionary would change to contain different paths to the same structures. However, the caller still need only request element using index 3 for the third account. The new dictionary contains the proper path.
Therefore, even if the data structure changes, the call for a predetermined element need not change. Additionally, because the lookup engine may be implemented on the server with only a request and a single element data response flows across the Internet instead of the entire data structure, significant performance improvements may be attained. The flowchart of FIG. The two button-handlers communicate via a boolean flag called stop. The stop-button handler sets the stop flag; while the start-button handler checks if stop flag has been set before continuing the next count.
This is because many of the GUI components are not guaranteed to be thread-safe. Channeling all accesses to GUI components in a single thread ensure thread safety. Suppose that we run the constructor directly on the main method under the "main" thread , as follow:. Instead of using the event-dispatching thread to do the compute-intensive counting, let's create a new thread to do the counting, instead of using the EDT, as follows:. A new thread is created by sub-classing the Thread class, with an anonymous inner class. We override the run method to specify the running behavior of the thread, which performs the compute-intensive counting.
An instance is created. Invoking the start method of the instance causes the run to execute on its own thread. The details on creating new thread will be explained later. The responsiveness improves slightly.
- Typical array-processing code..
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But the proper counter value is still not shown, and there is a delay in response to the "STOP" button. You may not see the difference running with a dual-core processor. This is because the counting thread does not voluntarily yield control to the EDT. Nonetheless, the JVM may force the counting thread to yield control according to the scheduling algorithm, which results in delay on updating the display TODO: When the "START" button is clicked, a new thread called "Thread- n " n is a running number is created to run the compute-intensive counting-loop.
However, this thread is not programmed to yield control to other threads, in particular, the event-dispatching thread. This program is, however, slightly better than the previous program. The display is updated, and the clicking of "STOP" button has its effect after some delays. Let's modify the program by making a call to the counting-thread's sleep method, which requests the counting-thread to yield control to the event-dispatching thread to update the display and response to the "STOP" button. The counting program now works as desired.
The sleep method also provides the necessary delay needed. The sleep method suspends the current thread and put it into the waiting state for the specified number of milliseconds. Another thread can begin execution in a single CPU environment. The sleep can be interrupted by invoking the interrupt method of this thread, which triggers an InterruptedException - this is unusual! In this case, the thread created to do the counting "Thread-n" yields control voluntarily to other threads after every count via the " sleep 10 ". This allows the event-dispatching thread to refresh the display as well as processing the "STOP" button after each count.
SwingWorker class, which can be used to run compute-intensive tasks in background threads, and passes the final result or intermediate results back to methods that run on the event-dispatching thread. We shall discuss SwingWorker in the later section. The second method is needed as Java does not support multiple inheritance.
If a class already extends from a certain superclass, it cannot extend from Thread , and have to implement the Runnable interface. The second method is also used to provide compatibility with JDK 1. It should be noted that the Thread class itself implements the Runnable interface.
The run method specifies the running behavior of the thread and gives the thread something to do. You do not invoke the run method directly from your program. Instead, you create a Thread instance and invoke the start method. The start method, in turn, will call back the run on a new thread.
Runnable declares one abstract method run , which is used to specify the running behavior of the thread:. The first two constructors are used for creating a thread by sub-classing the Thread class. The next two constructors are used for creating a thread with an instance of class that implements Runnable interface. The class Thread implements Runnable interface, as shown in the class diagram.
As mentioned, the method run specifies the running behavior of the thread. You do not invoke the run method explicitly. Instead, you call the start method of the class Thread. If a thread is constructed by extending the Thread class, the method start will call back the overridden run method in the extended class. On the other hand, if a thread is constructed by providing a Runnable object to the Thread 's constructor, the start method will call back the run method of the Runnable object and not the Thread 's version.
Often, an inner class named or anonymous is used instead of a ordinary subclass. This is done for readability and for providing access to the private variables and methods of the outer class. A class called MyThead is created by extending Thread class and overriding the run method.
A constructor is defined to takes a String as the name of the thread. The run method prints 1 to 5, but invokes yield to yield control to other threads voluntarily after printing each number. Take note that the output is indeterminate different run is likely to produce different output , as we do not have complete control on how the threads would be executed. Again, an inner class named or anonymous is often used for readability and to provide access to the private variables and methods of the outer class.
The stop , suspend , and resume methods have been deprecated in JDK 1. There are two kinds of threads, daemon threads and user threads. A daemon thread can be set via the setDaemon boolean on method. A daemon thread is an infrastructure thread, e. The JVM exits when the only threads running are all daemon threads. In other words, the JVM considers its job done, when there is no more user threads and all the remaining threads are its infrastructure threads.
The thread is in the "new" state, once it is constructed. In this state, it is merely an object in the heap, without any system resources allocated for execution. From the "new" state, the only thing you can do is to invoke the start method, which puts the thread into the "runnable" state. Calling any method besides the start will trigger an IllegalThreadStateException. The start method allocates the system resources necessary to execute the thread, schedules the thread to be run, and calls back the run once it is scheduled.
This put the thread into the "runnable" state. Hence, in the "runnable" state, the thread may be running or waiting for its turn of the CPU time. A thread cannot be started twice, which triggers a runtime IllegalThreadStateException. A thread is in a "terminated" state, only when the run method terminates naturally and exits.
The method isAlive can be used to test whether the thread is alive. The isAlive returns false if the thread is "new" or "terminated". It returns true if the thread is "runnable" or "not-runnable". This method returns an nested enum of type Thread. JVM implements a fixed priority thread-scheduling scheme. Each thread is assigned a priority number between the Thread.
The higher the number, the higher is the priority for the thread. When a new thread is created, it inherits the priority number from the thread that created it.
Multithreading & Concurrent Programming
You can used the method setPriority to change the priority number of a thread as follows:. The int priority is JVM dependent. It may take a value between 1 lowest priority to JVM chooses the highest-priority thread for execution. If there is more than one thread with the same highest-priority, JVM schedules them in a round-robin manner. JVM also implements a preemptive scheduling scheme.
In a preemptive environment, if at any time a higher priority thread becomes "runnable", the current lower priority thread will yield control to the higher priority thread immediately. If there are more than one equal-priority runnable threads, one thread may run until the completion without yielding control to other equal-priority threads.
This is known as starvation. Therefore, it is a good practice to yield control to other equal-priority thread via the sleep or yield method. However, you can never yield control to a lower-priority thread. In some operating systems such as Windows, each of the running thread is given a specific amount of CPU time. It is known as time slicing to prevent a thread from starving the other equal-priority threads.
However, do not rely on time slicing, as it is implementation dependent. An important point to note is the thread scheduling and priority is JVM dependent. This is natural as JVM is a virtual machine and requires the native operating system resources to support multithreading. Most JVM does not guarantee that the highest-priority thread is being run at all times. It may choose to dispatch a lower-priority thread for some reasons such as to prevent starvation. Therefore, you should not rely on the priority in your algorithm.
A monitor is an object that can be used to block and revive thread. It is supported in the java. Object root class, via these mechanisms:. Each Java object has a lock. At any time, the lock is controlled by, at most, a single thread. You could mark a method or a block of the codes with keyword synchronized.
Multithreading and Concurrency - Java Programming Tutorial
A thread that wants to execute an object's synchronized code must first attempt to acquire its lock. If the lock is under the control of another thread, then the attempting thread goes into the Seeking Lock state and becomes ready only when the lock becomes available. When a thread that owns a lock completes the synchronized code, it gives up the lock.
Synchronization can be controlled at method level or block level. Variables cannot be synchronized. You need to synchronized the ALL the methods that access the variables. You can also synchronized on static methods. In this case, the class lock instead of the instance lock needs to be acquired in order to execute the method. It is important to note that while the object is locked, synchronized methods and codes are blocked. However, non- synchronized methods can proceed without acquiring the lock. Hence, it is necessary to synchronize all the methods involved the shared resources.
For example, if synchronized access to a variable is desired, all the methods to that variable should be synchronized.