SCJP Sun Certified Programmer for Java 5 Study Guide (Exam 310-055) (Certification Press)

2017-07-07 02:10:07

Here are some of the key points from each section in this chapter.

Relational operators always result in a boolean value (true or false).

There are six relational operators: >, >=, <, <= , ==, and !=. The last two ( == and ! = ) are sometimes referred to as equality operators.

When comparing characters, Java uses the Unicode value of the character as the numerical value.

Equality operators

q	There are two equality operators: == and !=.
q	Four types of things can be tested: numbers, characters, booleans, and reference variables.

When comparing reference variables, == returns true only if both references refer to the same object.

q	instanceof is for reference variables only, and checks for whether the object is of a particular type.
q	The instanceof operator can be used only to test objects (or null) against class types that are in the same class hierarchy.
q	For interfaces, an object passes the instanceof test if any of its superclasses implement the interface on the right side of the instanceof operator.

q	There are four primary math operators: add, subtract, multiply, and divide.
q	The remainder operator (%), returns the remainder of a division.
q	Expressions are evaluated from left to right, unless you add parentheses, or unless some operators in the expression have higher precedence than others.
q	The *, /, and % operators have higher precedence than + and -.

q	If either operand is a string, the + operator concatenates the operands.
q	If both operands are numeric, the + operator adds the operands.

q	Prefix operators (++ and --) run before the value is used in the expression.
q	Postfix operators ( + + and --) run after the value is used in the expression.
q	In any expression, both operands are fully evaluated before the operator is applied.
q	Variables marked final cannot be incremented or decremented.

Returns one of two values based on whether a boolean expression is true or false.

q	Returns the value after the ? if the expression is true.
q	Returns the value after the : if the expression is false.

q	The exam covers six "logical" operators: &, \|, ^, !, &&, and \| \|.
q	Logical operators work with two expressions (except for !) that must resolve to boolean values.
q	The && and & operators return true only if both operands are true.
q	The \| \| and \| operators return true if either or both operands are true.
q	The && and \| \| operators are known as short-circuit operators.
q	The && operator does not evaluate the right operand if the left operand is false.
q	The \| \| does not evaluate the right operand if the left operand is true.
q	The & and \| operators always evaluate both operands.
q	The ^ operator (called the "logical XOR"), returns true if exactly one operand is true.
q	The ! operator (called the "inversion" operator), returns the opposite value of the boolean operand it precedes.

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