Overview and Java Review

This class is designed to introduce you to intermediate-level programming concepts. You will practice and apply these concepts by developing intermediate-level programs in Java. Though you may hear lots of people refer to this class as a Java programming class, the goal of this class is not simply to teach you how to write Java programs. Rather, you should come away with a firm understanding of general problem solving concepts that you can apply broadly. Similarly, this class should provide you with the foundation to easily learn and utilize any programming language, not just Java.

Java Basics

A variable is a name for a location in memory used to hold a data value. (L&L pp. 66)

The value stored in a variable may change. A variable is declared as follows:

int a;
double b, c;

A variable's type may be any of the 8 primitive types. The 8 primitive types are int, double, float, char, byte, boolean, long, and short. A variable may also refer to an object. Strings are a common example of this.

The class used to define an object can be thought of as the type of an object. (L&L pp. 114).

Initialization is the process of assigning an initial value to a variable. Following is an example assignment statement that assigns the value 5 to the variable a and example statement that declares the variable b and assigns it the value 9.4.

a = 5;
double b = 9.4

Recall that the single equals sign is often read as gets the value of (i.e, a gets the value of 5).

== compares the values stored in two variables. When used to compare two primitive values, it will evaluate to true if the values are the same and false otherwise. When used to compare two references, it will evaluate to true if the references refer to the exact same memory location. To evaluate the actual object contents, .equals is often used.

Casting is used to convert a variable of one type into a variable of another type. For example, you might cast a variable of type int to be a variable of type double in order to ensure that the result of dividing an int by an int is a floating point number.

int a = 5;
int b = 2;
double c = a/b; //no casting used, c is 2.0
double d = (double)a/b; //casting used, d is 2.5

Java has three types of loops: for, while, and do-while.

for loops are often used to execute a set of statements a predetermined number of times. The initialization, condition, and update are all written in the header of the loop.

for(int i = 0; i < 10; i++) {
        System.out.println(i);
}

while loops execute a set of statements until some general condition becomes false. The initialization of the control variable occurs prior to the loop, the condition is checked before the loop body is ever executed, and the update must appear in the loop body. You can always rewrite a for loop to be a while loop and vice versa.

int i = 0;
while (i < 10){
        System.out.println(i);
        i++;
}

do-while loops are different from for and while loops in that the body of a do-while loop always executes at least once. The control variable must be initialized outside of the loop, the body of the loop executes once before the condition is checked, and the update must occur in the loop body.

int i = 0;
do {
	System.out.println(i);
	i++;
} while(i < 10);

The dot operator enables access to the members of an object. Most commonly, the dot operator is used to invoke methods on an object.

String s = "Hello";
int length = s.length();

Overloading refers to having two methods with the same name but different signatures.

void printGreeting(String firstname) {
    System.out.println("Hello, " + firstname);
}

void printGreeting(String firstname, String lastname) {
    System.out.println("Hello, " + firstname + " " + lastname);
}

Overview and Java Review

Computer Science 112 - Introduction to Computer Science II

Java Basics