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45 Cards in this Set
- Front
- Back
Assume a class BankAccount has been created, and the following statement correctly creates an instance of the class:
BankAccount account = new BankAccount(5000.0); What is true about the following statement? System.out.print(account); |
the account object's toString method will be called.
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Giving the following Java statement, which statement will write"Eagle" to the file DiskFile.txt?
PrintWriter diskOut = new PreintWriter("DiskFile.txt"); |
diskOut.println("Eagle");
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When using the DecimalFormat class, which of the following will .1359 to 013.6%?
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000.0%
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What will be returned from a method, if the following is the method header?
public Rectangle getRectangle() |
the address of an object of the Rectangle class
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To compare two objects in a java class you must____.
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write an equals method that will make a field comparison of the two objects.
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What will generate a random number from 0 -1.0?
Random rand = new Random(); |
System.out.print(rand.nextDouble());
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What is the import statement for PrintWriter?
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import java.io.*;
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What will the following output return?
Scanner keyboard = new Scanner(System.in); String filename; System.out.print("Enter the filename: "); filename = keyboard.readString(); PrintWriter outFile = new PrintWriter(filename); |
Nothing. There is a syntax error.
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You have a defined a class CheckingAccount with a public static field named account and created a CheckingAccount object referenced by the variable, bankAccount. Which of the following will reference the account?
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CheckingAccount.account;
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What will open a file named MyFile.txt and allow you to read data from it?
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File fileName = new File("MyFile");
Scanner inputFile = new Scanner(fileName); |
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How is an object created from a class?
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import java.util.Random;
Random randomNumbers= new Random(); |
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Methods of the Random Class
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nextInt(int n) - T
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Use three useful methods from the math class?
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Math.pow();
Math.sqrt(); Math.PI Math.rnd(); |
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What does the JOptionPane class do?
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Allows you to display a message or input
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• Give the method for the JOptionPane to display output?
Give an example? |
JOptionPane.showMessageDialog
JOptionPane.showMessageDialog(null, “Hello World”); |
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Parse Methods
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// Store 2599 in iVar.
Int iVar = Integer.parseInt(“2599”); |
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DecimalFormat class
What does the # sign mean? |
suppresses zeros
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What does the zero mean in that format?
i |
t means that is will display the position but if the # sign is there it will suppress the decimal.
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What’s the difference between an input file and an output file
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Input a file in which you would input data…read data
Output a file into which you would write a file from your data. |
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What’s the import statement that you need in an file operation?
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import java.io*;
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static fields and static methods are also known as _____.
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Class fields or class methods.
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To invoke a static method or use a static field, ______, rather than the object name, is used.
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the class name
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When a class contains a static method, it is not necessary to create an ________.
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instance of the class in order to use the method
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static methods may not communicate with instance fields, only_______.
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static fields
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Normally, each object has its own data space, but if a variable is declared as static, only ______ of the variable exists
private static int count; |
one copy
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An object reference variable that does not currently point to an object is called a________.
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null reference
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The reserved word null can be used to explicitly set a null reference:
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name = null;
or if (name == null) System.out.println("Invalid"); |
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The _____ reference is simply a name that an object can use to refer to itself.
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this
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The _______ reference can be used to allow a parameter to have the same name as an instance field.
public void setLength(double length) { this.length = length; } |
this
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The _______ method of a class can be called explicitly: (distance is an object of the FeetInches class)
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toString()
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an example of String method being used:
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System.out.println("The distance you entered is "
+ distance.toString()); |
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An example of the the toString() method does not have to be called explicitly but is called implicitly whenever you concatenate an object of the class with a string:
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System.out.println("The distance you entered is "
+ distance); |
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All objects have a toString() method that returns______ & ______ of the object.
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the class name
a hash of the memory address |
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When objects are no longer needed they should be _____.
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destroyed
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The _______ will reclaim memory from any object that no longer has a valid reference pointing to it.
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garbage collector
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Instead of using the == operator to compare two objects, we should use the _____.
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equals method
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The equals method will compare objects by their _______ rather than by their memory addresses.
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contents
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Java uses the method signature (name, type of parameters and order of parameters) to determine which method to call?
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Overloaded method
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Operations performed by the I/O classes may throw an _______.
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IOException
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An example of throws IOException:
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public static void main (String[] args) throws IOException
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input file name is stored in variable file
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String line, file = "inventory.txt";
File openFile = new File (file); Scanner inFile = new Scanner (openFile); |
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The _____ class is used to open the input file.
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File
nextLine method is from Scanner class |
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When reading text tiles, an example that reads reads one line of text file as String data and stores it in the variable line:
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line = inFile.nextLine();
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_________________ creates a loop which will iterate until all the lines of the file are read:
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while (inFile.hasNext())
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An example of closing a file:
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inFile.close();
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