Expressions and Operations in Java

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Expressions and Operations
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This gives the following result:
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NaN == NaN false, NaN != NaN true, NaN > NaN false, NaN < NaN false NaN > 1000 false, NaN < 1000 false
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Because NaN cannot even be compared to itself, the only way to determine whether the variable v holds the value NaN is to call visNan() Infinity The result of performing arithmetic operations on infinity is either infinity or NaNThe following code shows examples of operations that return each of these results:
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var inf:Number = 10/00; println("inf + 1: {inf + 1}, inf "inf - inf: {inf - inf}, println("inf / 2: {inf / 2}, inf "inf mod 1000: {inf mod + inf: {inf + inf}," inf / inf: {inf / inf}"); mod inf: {inf mod inf}," 1000}");
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The result of running this code is as follows:
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inf + 1: Infinity, inf + inf: Infinity, inf - inf: NaN, inf / inf: NaN inf / 2: Infinity, inf mod inf: NaN, inf mod 1000: NaN
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Unlike NaN, it is possible to compare infinity to other values:
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var posInf:Number = 10 / 00; var negInf:Number = -10 / 00; println("posInf > negInf {posInf > negInf}," "posInf > 1000 {posInf > 1000}," "negInf < 1000 {negInf < 1000}"); println("posInf == negInf {posInf == negInf}," "posInf == posInf {posInf == posInf}," "negInf == negInf {negInf == negInf}");
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The results are as you might expect:
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posInf > negInf true, posInf > 1000 true, negInf < 1000 true posInf == negInf false, posInf == posInf true, negInf == negInf true
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Boolean Operations
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The operators and and or require two Boolean operands and produce a Boolean result:
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The and operator evaluates to true if both of its operands are true, otherwise to false The or operator evaluates to true if either of its operands is true and to false if they are both false
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6 Expressions, Functions, and Object Literals
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The and operator is equivalent to && in Java, whereas or is the same as || JavaFX does not have any equivalent of Java s bitwise logical operators & and | and neither does it have an exclusive or operator Both operators evaluate their operands only if it is absolutely necessary to do so For example, consider the following two functions, both of which return a fixed Boolean value (functions are discussed later in this chapter):
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function one() { return true } function two() { return false }
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The following expression evaluates to false because the second operand has value
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false: one() and two()
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To determine this, both functions need to be invoked However, if the expression were written in the following way, only the function two() would be called, because it returns false, and if either operand of the and operator returns false, the overall result is false:
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two() and one()
There is, therefore, no need to invoke function one() in this case Similarly, in this case, it is only necessary to invoke function one() to determine that the result should be true, and function two() will not be called at all
one() or two()
If function one() had returned false, however, it would have been necessarry to invoke function two() to determine the result of the operation The unary not operator evaluates to true if its operand is false and to false if its operand is true:
var value = true; value = not value; value = not value; // value is now false // value is now true
The not operator is more tightly binding than and, which is itself more tightly binding than or The == and != operators when applied to Boolean operands produce the obvious results:
false == false true == true false != true true != false
Object and Class Operations
Various operators can be applied to a Java or JavaFX class or to an object instance
Expressions and Operations
Object Creation The new operator creates and initializes a Java or JavaFX object given its classname When you are creating a Java object, parameters may be passed to its constructor3:
// A JavaFX Stage var stage = new javafxstageStage(); // A Java label Note the constructor parameter var javaLabel = new javaxswingJLabel("Label");
As you have already seen, the preferred way to create and initialize a JavaFX object is to use an object literal, supplying initial values for its properties:
import javafxstageStage; var stage = Stage { title: "Stage Title" visible: true };
Object literals are discussed further in the Object Literals section at the end of this chapter Function Invocation As you saw in the Invoking Java Functions section in 5, the operator can be used to invoke a function member of a JavaFX object or a method of a Java objectThe function may require arguments and may return a value:
var stage = javafxstageStage {}; // Invoke the close() function of the JavaFX Stage object stageclose();
Functions are discussed later in this chapter The as Operator The as operator is the equivalent of a cast in Java:
import javafxsceneNode; import javafxscenetextText; var node:Node = Text {}; var text:Text = node as Text;
As noted in 4, A Simple JavaFX Application, although you can use new to create a JavaFX object, it is more usual to use an object literal Unlike a Java class, a JavaFX class does not have a constructor, and therefore you cannot supply arguments if you choose to create a JavaFX object using the new keyword