Chapter 14
Primitive Operations and Expressions

14.1 Background

• Data types consist of values and operations.
• Values provide means to access data, and operations provide the means to process data.
• In the case of class data types, the values are represented by objects and the operations by methods.
• In the case of primitive data types, the values are represented by literals and the operations employ special notations.
• In appearances, the values and operations of the primitive data types are distinguished from those of the class data types. In nature, they are quite similar.
• The operators of the primitive data types correspond to the non-void methods of classes, and the operands correspond to the arguments.
• Like non-void methods, the operators perform some task and return a value.
• The ‘String’ class data type is distinguished in having literals and a primitive operation, namely ‘+’, built-in for it.

14.2 Assignment Operations

• Store data within variables
• Parameters are assigned the arguments provided by the invocations to the method names.
• Fields and local variables are assigned values through the assignment operation ‘=’.
• The assignment operation ‘=’ has a returned value. The returned value is the one supplied by the right term
• The assignment operation ‘=’ has a right-to-left precedence order
  x = y =15; 
  
• The assignment operation is overloaded to operate on the operands of primitive data types, and on the pointers of objects.
  int a;       a = 10; 
  double b;    b = 10.0; 
  

14.3 Type Conversion

• Through overloading
  double a; 
  a = 10; 
  
• By casting
  double a; 
  a = (double) 15; 
  
• Overloading is governed by an upward promotion criteria for the right operand toward the type of the left operand.
  1. Between integers: byte, short, int, long
  2. Between decimals: float, double
  3. Integers to decimals: long, float
  4. Characters to integers: char, int
  class prg { 
    public static void main ( String[] args ){ 
      char c = 'X'; 
      int i = c; 
      System.out.println( i );    // 88 
  } } 
  
• Overloading also follows a degrading criteria for the cases that the right operands are int and double literals.
  class prg { 
    public static void main ( String[] args ){ 
      char c = 88; 
      System.out.println( c );    // 'X' 
  } } 
   
  
• Downward casting may cause loss of content.
  class prg { 
    public static void main ( String[] args ){ 
      int i = 1100; 
      byte b = (byte) i; 
      System.out.println( b );    // 76 
  } } 
  

14.4 Arithmetic Operators

• Notation: ‘+’, ‘-’, ‘*’, ‘/’, ‘%’ (remainder)
  int i = 1; 
  i = i + 7 - 3; 
  
• In integer divisions, the fraction part is lost (‘3 / 2’ equals 1, and ‘2 / 3’ equals 0).
• The remainder operation applies only to integer values (‘3 / 2’ equals 1, and ‘2 / 3’ equals 2)..
• The operands are overloaded to deal with mixed-types operands, using the upward promotion and degrading criteria.
• The multiplicative operators have priority over the additive operators
• Within the multiplicative and additive operators, left-to-right precedence holds.
• Parentheses may be used to alter the precedence of operations
• The ‘+’ operator allows also operands of the ‘String’ class type. It is a generalization of the ‘concat’ method of the String class.
   "first string" + ", second string" 
  
  The operator promotes other types to strings, in mixed expressions. In the case of non-primitive types, the promotion is determined by the ‘toString’ method available for the class.
  "xx"+ 55 
  

14.5 Comparison Operations

• ‘>’, ‘>=’, ‘<’, ‘<=’, ‘==’, ‘!=’

14.6 Boolean Operations

• ‘&&’, ‘||’, ‘!’

14.7 Short Cuts

‘+=’, ‘-=’, ‘*=’, ‘/=’, ‘%=’, ‘++’, ‘--’

14.8 Initialization of Parameters and Returned Values

• Obey conversions rules similar to those that apply to the assignment operator ‘=’.

14.9 Assignment #18: Primitive Data Types

Due: We, May 28, midnight

1. Download the lab18a.java program from the given web page, and provide to the method tick the needed code for advancing the recorded time by one minute. The program should produce the following output.
   time =   1:05 
   time =  10:15 
   time =   0:00 
   time =   1:00 
   
2. The equations for deriving the coordinates (x_h,y_h) of the hour hand of a clock, and the coordinates (x_m,y_m) of the minutes hand, are as follows.
   

   In the equations, R_h and R_m denote the lengths of the clock hands, and (x,y) denotes the coordinates of the center of the clock.

   Download the lab18b.java program from the given web page. Provide the missing code in the calc method, so that it will compute the coordinates of the clock hands.

   For instance, the time 8:50 and the values x = 80, y = 80, and r = 60, imply x_h = 50.1, y_h = 82.6, x_m = 41.0, and y_m = 57.5 for clock hands of length r/2 and 3r/4. Similarly, the time 5:20 implies the values of x_h = 90.3, y_h = 108.2, x_m = 118.9, and y_m = 102.5.

3. Download the clock.java program from the given web page, replace there the comments /* code from tick */ and /* code from calc */ with the code introduced to the tick and calc methods, and then compile and execute the program.

   Just for the fun of it, can you improve the look of the analog clock?

Assume ‘lab18’ for the submit command, and submit your clock clock.java program.

Note: Files that fail to compile, and execute when applicable, will not be examined. They will be awarded a grade of 0 points.

Q&A

14.10 Assignment #19: Primitive Data Types

Due: Fr, May 30, midnight

1. Implement the ‘Compute’ class whose interface is given.
   class Compute { 
     static boolean cast(int, int, int); 
     static boolean equal(int, int, int); 
     static int interest(int, int, int); 
     static double root(int, int, int); 
     static boolean sign(int, int, int); 
   } 
   
   • A call to ‘interest(amount, rate, years)’ should return the value of

   • A call to ‘root(a,b,c)’ should return the root of the equation ax² + bx + c.

   • A call to ‘sign(a,b,c)’ should return a true value if and only if exactly two arguments have positive values.

   • A call to ‘equal(a,b,c)’ should check whether the sum of any two arguments can equal the third argument.

   • A call to ‘cast(a,b,c)’ should check whether any of the arguments can be stored in a variable of type ‘byte’.

   When used by the program

   class prg { 
     public static void main ( String [] args ){ 
       int v = Compute.interest(1000,8,2);System.out.println( v ); 
       double d = Compute.root(1,-5,6);   System.out.println( d ); 
       boolean b = Compute.sign(1,2,3);   System.out.println( b ); 
       b = Compute.equal(1,2,3);          System.out.println( b ); 
       b = Compute.cast(127,128,129); System.out.println( b ); 
       b = Compute.cast(128,128,128); System.out.println( b ); 
   } } 
   
   the output should be as follows.
   1172 
   3.0 
   false 
   true 
   true 
   false 
   
2. Download the calc.java program from the given web page, add to it the ‘Compute’ class, and then compile and execute the program.

Assume ‘lab19’ for the submit command, and submit your ‘calc.java’ program.

Note: Files that fail to compile, and execute when applicable, will not be examined. They will be awarded a grade of 0 points.

Q&A