visual basic barcode program 3: Operators and Assignments in Java

Making PDF417 in Java 3: Operators and Assignments

3: Operators and Assignments
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8. Because the first operand in the || expression on line 6 is false, the || operator can t skip the second operand; there s still a chance the expression can be true, if the second operand evaluates to true. 9. The isItSmall(9) method is invoked and prints i greater than 5 . 10. The isItSmall(9) method returns false, so the expression on line 6 is false, and thus line 7 never executes. The || and && operators only work with boolean operands. The exam may try to fool you by using integers with these operators, so be on guard for questions such as,
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if (5 && 6) { }
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where it looks as though we re trying to do a bitwise AND on the bits representing the integers 5 and 6, but the code won t even compile.
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Logical Operators (not Short-Circuit)
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The bitwise operators, & and |, can also be used in logical expressions. But because they aren t the short-circuit operators, they evaluate both sides of the expression, always! They re inefficient. For example, even if the first operand (left side) in an & expression is false, the second operand will still be evaluated even though it s now impossible for the result to be true! And the | is just as inefficient; if the first operand is true, it still plows ahead and evaluates the second operand even when it knows the expression will be true. The rule to remember is The short-circuit operators (&& and ||) can be used only in logical (not bitwise) expressions. The bitwise operators (& and |) can be used in both logical and bitwise expressions, but are rarely used in logical expressions because they re not efficient.
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You ll find a lot of questions on the exam that use both the short-circuit and non-short-circuit logical operators. You ll have to know exactly which operands are evaluated and which are not, since the result will vary depending on whether the second operand in the expression is evaluated. The Self Test at the end of this chapter includes several logical operator questions similar to those on the exam.
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Now that you have a better idea how operators work in Java, the following chart shows some operators in action:
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Passing Variables into Methods (Exam Objective 5.4)
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SCENARIO & SOLUTION
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What is the result of (1 & 3) What is the result of (1 | 3) What is the result of (1 << 2) What is the resulting value of (new String( fred ) instanceof Object) 1 3 4 true
CERTIFICATION OBJECTIVE
Passing Variables into Methods (Exam Objective 5.4)
Determine the effect upon objects and primitive values of passing variables into methods and performing assignments or other modifying operations in that method. Methods can be declared to take primitives and/or object references. You need to know how (or if) the caller s variable can be affected by the called method. The difference between object reference and primitive variables, when passed into methods, is huge and important. To understand this section, you ll need to be comfortable with the assignments section covered in the first part of this chapter.
Passing Object Reference Variables
When you pass an object variable into a method, you must keep in mind that you re passing the object reference, and not the actual object itself. Remember that a reference variable holds bits that represent (to the underlying VM) a way to get to a specific object in memory (on the heap). More importantly, you must remember that you aren t even passing the actual reference variable, but rather a copy of the reference variable. A copy of a variable means you get a copy of the bits in that variable, so when you pass a reference variable, you re passing a copy of the bits representing how to get to a specific object. In other words, both the caller and the called method will now have identical copies of the reference, and thus both will refer to the same exact (not a copy) object on the heap.
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