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Cross Ref > Operators

By Mike Prestwood

Java versus Corel Paradox: A side by side comparison between Java and Corel Paradox.

 
Operators
 

A language symbol used for assignment, comparison, computational, or as a logical.

Assignment

[Other Languages] 

Languages Focus

Common assignment operators for languages include =, ==, and :=. An assignment operator allows you to assign a value to a variable. The value can be a literal value like "Mike" or 42 or the value stored in another variable or returned by a function.

Java:   =

Java uses = for it's assignment operator.

Corel Paradox:   =

ObjectPAL uses = for it's assignment operator.

Syntax Example:  
var
 FullName String
   Age SmallInt
endVar
  
FullName = "Randy Spitz"
Age = 42




Comparison Operators

[Other Languages] 

General Info: Round Floating Point Numbers

When comparing floating point numbers, make sure you round to an acceptable level of rounding for the type of application you are using.

Languages Focus

A comparison operator compares two values either literals as in "Hello" and 3 or variables as in X and Counter. Most languages use the same operators for comparing both numbers and strings. Perl, for example, uses separate sets of comparison operators for numbers and strings.

Java:   ==, !=

The Java comparison operators are:

== equal
!= not equal
< less than
> greater than
<= less than or equal
>= greater than or equal

More Info / Comment
Corel Paradox:   =, <>

Common comparison operators:

= equal
<> not equal
< less than
> greater than
<= less than or equal
>= greater than or equal

Syntax Example:
'Does ObjectPAL evaluate the math correctly? No!
If .1 + .1 + .1 = .3 Then
msgInfo("", "correct")
Else
msgInfo("", "not correct")
endIf




Empty String Check

[Other Languages] 

Languages Focus

An empty string is a zero length string, a string that is equal to null (""), or not assigned. In some languages, you can check if a string is empty by comparing it to an empty string (""). Some languages distinguish between nil and null ("") so checking if the length is 0 is easier.

Java:   IsEmpty
Corel Paradox:   isBlank() or not isAssigned()

In ObjectPAL, an empty variable can be unassigned (essentially null) or blank (equivalent to ""). You have to use both isBlank and isAssigned to check for an empty string.

Syntax Example:
var
 s String
endVar
  
;s = ""  ;Uncomment to test 2nd case.
 
if isBlank(s) or not isAssigned(s) Then
 msgInfo("", "empty string")
endIf




Logical Operators

[Other Languages] 

Languages Focus

Logical operators perform conditional and, or, and not operations. Some languages support both binary logical operators that link two and unary logical operators negate (make opposite) the truth value of its argument. Finally, some languages short circuit logic. For example, with this or that, if this is an expression returning true, then that is never executed.

Java: 

Java logical operators:

&& and, as in this and that
|| or, as in this or that
! Not, as in Not This
& boolean logical OR (not short circuited)
| boolean logical OR (not short circuited)
?: Ternary (short for if-then-else)
~ Unary bitwise complement
<< Signed left shift
>> Signed right shift
>>> Unsigned right shift
^ Bitwise exclusiv OR

Syntax Example:
//Given expressions a, b, c, and d:
if !((a && b) && (c || d)) {
  //Do something.
}
Corel Paradox: 

ObjectPAL logical operators:

and and, as in this and that
or or, as in this or that
Not Not, as in Not This

Like VBA, ObjectPAL never short circuits. Given the expression this or that as well as this and that, if this evaluates to false, then that is still executed.

Syntax Example:
;Given expressions a, b, c, and d:
if Not (a and b) and (c or d) then
  ;Do something.
endIf




String Concatenation

[Other Languages] 
Java:  "String Concatenation" + or append

In Java, you use either the String concatenation + operator or StringBulder class methods such as append. Since Java compilers frequently create intermediate objects when the + operator is used and don't when StringBuilder.append is used, the append method is faster than the + operator.

In general, use the convenience of a + operator when speed is not an issue. For example, when concatenating a small number of items and when code isn't executed very frequently. A decent rule of thumb is to use the + operator for general purpose programming and then optimize the + operator with StringBuilder.append as needed.

Syntax Example:

Simple + operator example:

System.out.println("Hello" + " " + "Mike.");

 

Using StringBuilder example:

StringBuilder myMsg = new StringBuilder();

myMsg.append("Hello ");
myMsg.append("Mike.");
 
System.out.println(myMsg);
Corel Paradox:  "String Concatenation" +

String literals s are limited to 255 characters but you can simply add two strings together as in:

s = "A long string." + "Another long string."
Syntax Example:
var
FirstName  String
  LastName  String
endVar
 
FirstName  = "Mike"
LastName  = "Prestwood"
msgInfo("", "Full name: " + FirstName + " " + LastName)




Unary Operators

[Other Languages] 

General Info: Unary Operator

An operation with only one operand (a single input). Common unary operators include + plus, - minus, and bitwise not. Some operators can function as both unary and binary operators. For example, + and - operators can serve as either.

Languages Focus

What unary operators are supported in additoin to the standard plus, minus, and bitwise not.

Java: 

An operation with only one operand (a single input). The Java unary operators are ++, --, +, -, ~, and !.

  • + Indicates positive value (numbers are positive without this)
  • - Negates an expression
  • ++ Increment operator by 1
  • -- Decrement operator by 1
  • ! Logical complement operator (inverts the value of a boolean)
  • ~ Bitwise inversion operator (works on integral data types)
More Info / Comment
Corel Paradox: 

The ObjectPAL unary operators are:

+
-
Not

More Info / Comment




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