Modify Common Object References In Lists - MyArrList And UrArrList
Jan 29, 2014
"What happens if you modify the common object references in these lists, myArrList and urArrList ? We have 2 cases here: In the first one, you reassign the object reference using either of the lists. In this case, the value in the second list will remain unchanged.In the second case, you modify the internals of any of the common list elements - in this case, the change will be reflected in both lists."
I have written the following code, which tests the first case mentioned above, and i get the output as expected: myarrList remains unchanged. How can i test the second case ? My thoughts are ....'second case is untestable the following code, because String is immutable. I need to use StringBuilder or something else to write code for test of second case mentioned'.
ArrayList<String> myarrList = new ArrayList<>();
myarrList.add("one");
myarrList.add("two");
ArrayList<String> urarrList = new ArrayList<>();
urarrList.add("three");
urarrList.add("four");
System.out.println("ArrayLists setup");
I am reading Head First: Java and got to Object References. In the book I got a little bit confused on what happens when two object reference's point at the same object so I wrote a small crude test, the below code. This of course clarified what happens but what I am interested in knowing is in what circumstances would you want to have two separate references for the same object when you could just use the original? Eg. v1
class ObjectValue{ int objVal = 1; } class ObjectValueTestDrive{ public static void main(String [] args){ // "Value of v# should be" refers to if it copied the given object values, instead of referencing the same object ObjectValue v1 = new ObjectValue(); System.out.println("Value of v1 should be 1:" + " "+ v1.objVal);
So I set out to write a program that takes two things from user: Name and Age
Then prints out "Name is Age"
I went through using a "launcher" and having a proper object: [URL]
The class names are Practice and Practice Launcher because I just use a Practice file as a sandbox environment so I understand its not correctly named. I also understand my comments aren't great but I'm just trying to make it work.
Practice.java public class Practice { //constructor public Practice (String a, int b) {
[Code]....
My Practice.userName doesnt reference the variable userName. Why is this?
Also y does this line need Practice twice? Practice Practice = new Practice(userName, 45);
I have to implement an object pool that uses phantom references to collect objects abandoned by client threads. This is what I have. I'm really not sure about this implementation.
class ObjectPool<T extends CloneableObject<T>> { private Queue<T> pool; private List references = new ArrayList(); private ReferenceQueue rq = new ReferenceQueue(); private CloneableObject<T> prototype
when a new object is created in Java it follows the idiom:
Object obj = new Object(); where the Object() constructor matches the object type Object.
But what if it doesn't? I understand from the Oracle Docs on creating objects and polymorphism that the constructor must be in that object's class or one of its subclasses. However, suppose we wanted to declare a new stack. My first instinct would be:
Stack s1 = new Stack(); But I assume it's valid to do it this way, too:
Object s2 = new Stack(); // Is there a difference here? What are we really saying about s2? I'm guessing s2 is simply an empty stack, but only has access to the Object class methods? I'm not sure why someone would ever do this, but I want to solidify my understanding of the Java hierarchy. Are there really any circumstances where someone would use a subclass's constructor when creating a new object?
I have two different "business objects", and they have multiple attributes in common(around 25 I believe, all of which are simply a String). Basically, these objects are used for documentation purposes on the same file.
The program can choose to update a given Document at any point in time, even if changes haven't been made to existing version. So what I'm trying to do, is check to see if these attributes differ any between the two files(the exisitng copy, and the new request). If so, I'll update...else I simply throw out the request. The workload can be rather intense at times so I don't want to bog down the system anymore then necessary.
Simply pulling down every attribute for each and comparing seems like a lot of overhead, any more efficient way to achieve these results?
lst contains list of objects and one of the objects contains the property bDate(Timestamp) which has the value 28-2-1989 00:00:00.0, now I just wants to change the value into 28-2-1989 and store it back into the List as a Timestamp. how can I do that.
I am trying to grab a graphical object from an arraylist, and reposition its coordinates on a Jframe when adding it. My program of course deals with strings, and once it sees specific words in my console, some method is called that adds, removes, or otherwises modifies certain objects on screen.
Here I want to say something like move(object[1],xpos,ypos) which will move a certain object from a specified point in the array, and move it to new x and y positions on the JFrame. I use a different class that extends a graphics program, so when I say add(something,x,y) it draws the object onscreen where I want it. These are some relevant, though incomplete, methods that should move an object already painted on screen:
Console class
Java Code:
public void doMoveCommand(String cmd, String arg, String xpos, String ypos) { int x = Integer.parseInt(xpos); int y = Integer.parseInt(ypos); if (cmd.equals("posMake") && arg.equals("star")) { box.moveStar(box.historyG.get(1), x, y); //historyG is an arraylist of GPolygons freeCommand();
[Code] ....
When I say makepos(whatever) I am getting a arraylist out of bounds exception. How I might be able to accomplish moving objects already on screen?
I have a design scenario here which is quite interesting and complex. I have a Java class structure as follows,
class A { class B; innerClass B { List<class C> listofC; innerClass C { String attribute1; String attribute2; // Their getter setters } } }
So I have this as an API. Now my challenge is that I need to add one more property to inner class C. i.e attribute3 in innerClass C. I need to do this without disturbing the code in class A by extending these classes or writing a new wrapper, so I can use class C with new properties .
I hope this should be achievable through any design pattern either at runtime or design time.
This program is basically complete. It compiles and runs. It is a college course assignment that I pretty much completed but for the last part in which I'm suppose to change the values of all fields and display the modified values using a toString method. Modifying the values of the fields is where I am stuck. I don't think I need to create a new text data file to do this. The instructor only asked that all the values of fields be changed and this was the last part of the assignment so I don't think it involves creating additional ObjectOutputStream and ObjectInputStream objects. I'm getting a NullPointerException error on line 161.Here is the code. I'm also including the input data file.
//create program so that objects of class can be serialized, implements interface Serialiable //create constructor with 4 parameters with accompanying get and set methods, Override toString method //create text file with 5 records, create Scanner object,ObjectOutputStream, and ObjectInputStream //create new ItemRecord object, change values of all fields in ItemRecord object using object's set methods //modify ItemRecord object using toString method
[hightlight =Java]import java.io.Serializable; public class ItemRecord implements Serializable
----jGRASP wedge2: exit code for process is 1. ----jGRASP: operation complete.
Here is the data file: A100 99.99 10 Canon PowerShot-135 A200 149.99 50 Panasonic-Lumix T55 A300 349.99 20 Nikon- D3200 DSRL A400 280.99 30 Sony- DSC-W800 A500 97.99 20 Samsung- WB35F
Here is the data file for the modified field values. B100 98.00 10 ABC1010 B200 97.00 15 DEF1020 B300 96.00 10 GHI1030 B400 95.00 05 JKL1040 B500 94.00 01 MNO1050
Modify class Time2 to include a tick method that increments the time stored in a Time2 object by one second. Provide method incrementMinute to increment the minute and method incrementHour to increment the hour. The Time2 object should always remain
a) incrementing into the next minute,
b) incrementing into the next hour and
c) incrementing into the next day (i.e., 11:59:59 PM to 12:00:00 AM).
how to manage case 4 stuff and what's the problem of this CODE.
import java.util.Scanner; public class Time2Test { public static void main( String args[] ) { Scanner input = new Scanner( System.in ); Time2 time = new Time2(); // input System.out.println( "Enter the time" ); System.out.print( "Hours: " ); time.setHour( input.nextInt() );
how to do a deep copy of objects that contain references. I am specifically wanting to make a deep copy of a tree. Logically, each tree node contain references to its children nodes. Here is the basics of my node class
public class BSTNode implements Comparable, Serializable {
I know I must only be making a shallow copy because when I make a copy of tree1, called tree2, and edit tree1 the edits also appear on tree2. Here is my copy method within my BSTNode class
public BSTNode copy() { BSTNode obj = null; try{ ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream out = new ObjectOutputStream(bos); out.writeObject(this); out.flush(); out.close();
[code]....
When I wish to copy the entire tree, I call that above copy method from my BSTree class using the methods below. (I have 2 methods because this is a homework assignment that requires a copy method that calls a preorder traversal method)
public BSTNode copy() { BSTNode copiedTreeRoot = new BSTNode(); return copyTree(copiedTreeRoot,root);
[code]....
And further along when I make changes to tree1, tree 2 also changes. I have no clue what I'm doing wrong. I believe it must be somewhere in how I return the new tree or something.I tried this edit to my copy method, but it made no difference.
public BSTNode copy() { BSTNode obj = null; try{ ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream out = new ObjectOutputStream(bos); out.writeObject(this);
So I have an array of objects, each with their own position, I tried switch the references in the array of two objects, then repainted (immediately), but the two objects aren't switching positions on screen...does this even work?
Which of these is not a real differentiator for programming languages:
a) Object-oriented / Process-Oriented b) Interactive / Automated c) Interpreted / Compiled d) Strongly-Typed / Weakly-Typed e) All of the above f) B and C g) B and D
Almost all support OOP, Interactive/Automated, Interpreted/Compiled but not sure about Strongly typed/Weakly typed.
I have two ArrayLists and I want to compare them for common elements, and based on the result I want to update the first Arraylist to only have these elements. sort of like the opposite of RemoveAll() which removes elements in common and keep the ones that are unique. so far I thought of using for loop and .contains() in case it was fault,element not present, remove from list. but I was wondering in what other ways, perhaps APIs i can use to do that?
I need to create an algorithm that finds the common element(s) in all arrays that has a signature of public Comparable[] findCommonElements(Object[] collection) that has an efficiency of at most O(knlogn), uses a query array, and accepts as input a collection of arrays. I am aware my time would be better spent learning how to use array lists and hash sets, but I am supposed to use concepts already covered, and these have not been.
I feel like this code should work, but it is returning null for the array of common elements. Which means it obviously is not working correctly. I am also likely going to need implementing the sort algorithm, but I wanted to get the part of finding the common elements set first.
public class CommonElements2<T extends Comparable<T>> { Comparable[] tempArr; Comparable[] common; Comparable[] queryArray; /* sort algorithm goes here */ public Comparable[] findCommonElements(Object[] collections)
I have developed a web portal using jsp and struts 2. I have approximately 10 JSP pages which looks exactly the same and have two text areas and two hidden fields. All 10 pages are exactly the same except for hidden field value. Can't i have a single common jsp page. How can i achieve it. A sample page i am attaching...
I am using the following regex - [a-zA-Z0-9]{9,18} which means I can use alphabets and numbers with minimum length as 9 and maximum length as 18.It should not take special characters.
It takes values like ADV0098890 etc. but it is also taking ADV0098890[] which is wrong.
//******************************************************************** // Demonstrates the existence of separate data space in multiple instantiations of a programmer-defined class. //********************************************************************
[code]....
Basically i'm trying to add one more "coin" to flip. My problem is that my if-else structure isn't working correctly here's what it looks like:
if (count1 < GOAL) if (count2 < GOAL) System.out.println("Coin 3 Wins!");
[Code] .....
It only works correctly when "coin2" wins.How would I modify my if else structure to get the output I am looking for?
