Expressions and Operations

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The operators that are supported by JavaFX are listed in Table 6-1, together with the data types that can appear as their operands Operators shown with a lower priority value in this table are more tightly binding than those with a higher priority valueThat means that given any pair of operators, the one that is higher up in the table is evaluated first For example, in the following expression, the multiplication operator has lower numerical priority than the addition operator and so is evaluated first, and the result of the expression is 23:

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3 + 4 * 5

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6 Expressions, Functions, and Object Literals

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Table 6-1 Priority

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JavaFX Operators Operator

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function() () new { object literal }

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A JavaFX function or Java method call An expression in parentheses Instantiates a new object Instantiates and initializes a new object Post-increment Post-decrement Pre-increment Pre-decrement Unary minus (as in -1) Logical negation Size of a sequence Reverse of a sequence Index of a sequence element Multiplication Division Remainder on division Addition Subtraction Equality Inequality Less than Less than or equal to Greater than Greater than or equal to Type checking Casting Logical AND Logical OR Add and assign Subtract and assign Multiply and assign Divide and assign Assignment

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Object/class N/A Object/class Object/class Numeric Numeric Numeric Numeric Numeric Boolean Sequence Sequence Sequence Numeric Numeric Numeric Numeric Numeric All All Numeric Numeric Numeric Numeric Object/class Object/class Boolean Boolean Numeric Numeric Numeric Numeric All

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++ (postfix) -- (postfix) ++ (prefix) -- (prefix) not sizeof reverse indexof

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* / mod

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+ == != < <= > >=

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7 8 9 10

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Expressions and Operations

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The default evaluation order can be changed by enclosing part of the expression in parentheses, like this:

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Parentheses are more tightly binding than arithmetic operations, so in this case, the addition is performed first and the result would be 35 In general, JavaFX operators behave in the same way as their Java counterpartsThe following sections briefly look at each of them, grouped by the category of data on which they operate, with the exception of the sequence operators, which are covered in 7, Sequences

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Numeric Operations

Each operand of a numeric operation must be one of the numeric types and the result will be either another numeric value or a Boolean, as described in the following sections For the sake of brevity, we refer to Byte, Short, Character, Integer, and Long as integer types and to Float, Number, and Double as floating-point types Arithmetic Operations JavaFX provides the same arithmetic operations as Java, with the same semanticsThe result of an arithmetic operation is always an integer type or a floating-point type, depending on the types of the operands:

n n n

If both operands are integer types, the result is an integer type If both operands are floating-point types, the result is a floating-point type If one operand is a floating-point type and the other is an integer type, the integer value is first converted to a floating-point value, the operation is performed, and the result will be a floating-point type

The following examples illustrate these rules:

var a = 1 + 2;

Integer, and

Because both operands are integers, the result type inferred for the variable a is the value assigned to it is 3

var b = 10 + 20;

In this case, both operands are Number types, so the type of b is Number, and the result is 30

var c = 10 + 2;

6 Expressions, Functions, and Object Literals

Here, the operands are of mixed types The integer value 2 is converted to the floatingpoint 20, and the inferred type of c is Number The result is 30

The +, -, *, and / operators do what you would expect them to do, unless the resulting value is too large or too small to be represented as an integer or floating-point type, an issue that is covered in the Range Errors in Arithmetic Operations section, later in this chapter The mod operator is the same as the Java % operator, returning the remainder of an integer division of the left operand by the right operand Here are some examples of these operators applied to operands that are Integer types:

var var var var var var a b c d e f = = = = = = 123 + 456; 456 - 123; 5 * 40; 40 / 5; 32 / 5; 32 mod 5; // // // // // // Result Result Result Result Result Result = = = = = = 579 333 200 8 6 2 (remainder on division by 5)

The value assigned to the preceding variable e is 6 rather than 64 because the result of an integer division is also an integerThe exact answer is truncated to produce 6The result of dividing 32 by 5 would be 6 because the result is always rounded toward 0 When one or both of the operands is a floating-point type, numeric operations are not always mathematically accurate, as the following examples illustrate:

var var var var var var a b c d e f = = = = = = 1234 + 2345; 1234 - 2345; 00001 * MathPI; 10/410; d * 41; 3E10 + 1E-10; // // // // // // Result Result Result Result Result Result = = = = = = 3579 -11110001 31415925742264873E-4 0024390243 099999994 30000001E10

As you can see, the subtraction on the second line results in a slightly inaccurate value being assigned to the variable b Errors like these occur because not all decimal fractional numbers can be accurately represented in the binary floating-point form used to represent the values of the Number type The value PI (defined by the class javafxutilMath) used in the expression 00001 * MathPI is of type DoubleAs a result, the whole expression evaluates to a Double, and the variable c will also be of type DoubleThis is why this particular result has more decimal places than the results of the other expressions, which are all of type Number The result shown for the operation 10/410 is 0024390243This is not the true mathemetical result in fact, it is accurate to only eight decimal placesWhen this result is multiplied by 41 on the next line of code, the small error in the division causes the result to be not quite 10, which would be the correct answer Small errors like this are common in floating-point arithmetic, and they accumulate, so that the more operations you