SCJP Sun Certified Programmer for Java 5 Study Guide(Chapter 4)

Operators

Relational Operators

• 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
  • There are two equality operators: == and !=.
  • 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.

Instanceof Operator

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

Arithmetic Operators

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

String Concatenation Operator

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

Increment/Decrement Operators

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

Ternary (Conditional Operator)

• Returns one of two values based on whether a boolean expression is true or false.
  • Returns the value after the ? if the expression is true.
  • Returns the value after the : if the expression is false.

Logical Operators

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

It is mostly from the McGraw Hill - SCJP Sun Certified Programmer for Java 5 Study Guide