1/3/08 Notes

To Notes

CSC 212 -- 1/3/08

Useful URLs:

This Web Site (CSC212 - Section 201 Course Web Site at www.depaul.edu/~sjost/csc212)
Links for Table of Contents at left.
BlueJ Website: www.bluej.org
The latest BlueJ version is 2.2.1.
TextPad Website: www.textpad.com
The latest TextPad version is 5.03.

Pretest

What are the meanings in Java for each of the following symbols?
Answers:
- Meanings for ;
  1. End of statement.
  2. Separates the parts of a for statement:
    for (int i = 1; i <= 20; i++)
- Meanings for +
  1. Addition of numeric variables +.
  2. String Concatenation of String variables +.
  3. Preincrement ++x.
  4. Postincrement x++.
  5. Addition assignment operator x += 2;.
  6. Concatenation assignment operator x += "abc";.
- Meanings for /
  1. Integer division: 3 / 2
  2. Floating point division: 3.0 / 2
  3. C++ style comment //
  4. C style comment /* ... */
- Meanings for =
  1. Assignment operator.
- Meanings for ==
  1. Equality comparison operator ==.
  2. Inequality comparison operator !=.
  3. Greater than or equal comparison operator >=.
  4. Greater than or equal comparison operator <=.
- Meanings for &
  1. Logical and && with short circuit evaluation.
  2. Logical and & with complete circuit evaluation.
  3. Bitwise and &.
  4. Bitwise and assignment operator &=.
- Meanings for %
  1. Mod operator % (Remainder from integer division).
  2. Assigment mod operator %=.
- Meanings for ( )
  1. Changing the order of precedence for operators: y = (2 + x) * 3;.
  2. Method call: System.out.println(x);.
  3. Condition in if, for, or while statements: if (x > 5)
  4. Casting: y = (int) 3.14159;
- Meaning for [ ]
  1. Array index such as a[i].
- Meaning for { }
  1. Delimiters for a block of code, such as the body of a method or of an if, for, or while statement.
Write Java code to create an array of int with elements 3, 7, and 9.
Answer: Recall that there are three steps to creating and using an array:
1. Declaring the array reference variable.
2. Creating the space for the array.
3. Assigning values for the array elements.
- Method 1. Do Steps i, ii, and iii separately.
  int[] a;
  a = new int[3];
  a[0] = 3; a[1] = 7; a[2] = 9;
- Method 2. Combine Steps i and ii.
  int [] a = new int[3];
  a[0] = 3; a[1] = 7; a[2] = 9;
- Method 3. Combine Steps i, ii and iii.
  int [] a = {3, 7, 9};
What are the rules for creating Java variable names?
Answer: Variable names must start with a letter and consist of letters and digits. They should not be more than about 15 characters long and should be a meaningful description of what the variable contains.
List some Java methods for input and output.
Answer: JOptionPane.showInputDialog, JOptionPane.showMessageDialog, System.out.print, System.out.println, System.out.printf. Some methods of the Scanner class are next, nextInt, nextDouble.

Some Input/Output Examples

See the Greeter1 Example (Greeter1.java).
Here are directions for compiling and running a Java source code file.
See the Greeter2 Example (Greeter2.java).

Java Datatypes

Here are the primitive Java datatypes:
byte short int long float double char boolean
See the document Java Constants, Variables, and Datatypes
Run the Datatypes Example: Datatypes.java.

Java Operators

See this table of Java Operators.
These are the the Java bitwise operators:
| & ^ ~

Binary and Hex Numbers

To understand bitwise operators, see how a computer represents integers in binary. See Binary and Hex Numbers.
Practice Exercises:
- Convert 79 and 117 to one byte binary.
- Convert 00110110 and 01101101 to decimal.
- Convert 29 and 62 to hex.
- Convert 3D and 6A to hex.
See the example Bitwise.java.

Project Proj1

See the description of Project Proj1.