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Java: Classes and Objects UPDATED ACTUAL Exam Questions
and CORRECT Answers
Declaring a method - class Myclass{ static void sayHello(){ //sayHello is the method System.out.println("Hello World!") } public static void main (String [ ] args) { sayHello(); sayHello(); sayHello(); } } /* output: Hello World! Hello World! Hello World! */ code reuse - You can write a method once, and use it multiple times, without having to rewrite the code each time Return value syntax - class MyClass {
static int sum(int val1, int val2) { return val1 + val2; } public static void main(String[ ] args) { int x = sum(2, 5); System.out.println(x); } } //output 7 *Note: The return is saying to add val 1 and val 2 (parameters), as you can see in the next function starting with public, there is a variable with x and the sum has (2,5) those two will be added due to the method prior Public - The class is accessible by any other class. Package - A group of similar types of classes Default - A variable or method declared with no access control modifier is available to any other class in the same package. Protected - Same as default, with the addition that subclasses can access protected methods and variables of the superclass (learn more about subclasses and superclass later) Private - Accessible only within the declared class itself
Reference variable - When you create an object using the constructor Math class - which provides predefined methods for mathematical operations Math.abs() - returns the absolute value of its parameter Math.ceil() - Rounds to nearest integer up when using double Math.max() - Rounds to the nearest integer down when using dobule Math.min() - Returns the smallest parameter Ex int m = Math.min(10, 20); // 10 Math.pow() - takes two parameters and returns the first parameter raised to the power of the second parameter ex double p = Math.pow(2, 3); // 8. sqrt() - square root sin() - sine cos() - cosine
final - Keeps a variable constant, any attempt to change it will cause an error ex. class MyClass { public static final double PI = 3.14; public static void main(String[ ] args) { System.out.println(PI); } } Packages - a group made up of similar types of classes, along with sub-packages OOP - Object-Oriented Programming Attributes - Characteristics in an object. For example, a car can be red or blue Behavior - Dependent on the object type Three dimensions in object oriented - Identity Attributes Behavior Class - Describes what an object will be. It is a blueprint, description, definition of an object Class syntax - Very beginning! public class (name class here) {
