CMSC131 Midterm #1

Object

The principal entities that are manipulated by a Java program

Class

A blueprint or template for the structure of an object. The structure around which all Java programs are based. A typical program has many classes.

Method

Java's term for a procedure or subroutine. Every method belongs to some class, and a class may have many methods

Main Method

There must be exactly one method called main. This is where execution begins.

public static void main(String args[]){

//body

}

Statements

Individual instructions. There are many different types of statements. Each method consists of some number of statements.

Declarations

(Ex of statement) Declare (and initialize) variables

Assignment

(Ex of statement) Compute and assign a new value to a variable

Method invocation

(Ex of statement) Execute a method (which may return a result)

Control flow

The order in which statements are executed. General rule is top to bottom.

What is Java compiled into?

Java bytecode

What do you need to run Java bytecode?

A bytecode interpreter ("Java Virtual Machine")

Why is Java more portable than C or C++?

C/C++ programs are compiled into machine code (rather than Java bytecode) and executed directly by CPU.

A class consists of a combination of data units, called \___________, and computation units, called \___________.

variables,

methods

Methods

Where all the computation takes place. Each method has a name, a list of arguments enclosed in parentheses, and body, enclosed in curly braces.

Ex:

public static void main (String[]args){

//body

}

Variables

Data items that the methods operate on. Can be of various types.

List all primitive variable types

8 types: byte, short, int, long, float, double, boolean, and char

What do expressions/operators do?

Manipulate variables

Ex:

x \= (2*y-z)/32

Comments

Used to indicate programmer's intent. Do not affect program's execution. There are line comments ( using // ) and block comments ( using /star ... star/ )

Debugging

Process of finding and fixing problems

"Compile time" errors

Caught by compiler.

Ex:

Syntax errors

Variable type errors

"Run time" errors

appears during program execution

Ex:

division by zero

semantic errors

Different types of data require \_________ \__________ of memory.

different amounts. The compiler's job is to reserve sufficient memory

Operations can only be performed between variables with \_____________ types.

compatible

Valid Variables Names

-Starts with: a letter (a-z or A-Z), or dollar sign ($), or underscore ( _ )

-Followed by: zero or more letter, dollar signs, underscores, or integers

-Cannot be any of reserved names (class, float, int, if, etc.)

Camel case

A capitalization style

Ex:

dataList

myFavoriteMartian

Variables start with \_______ case. Classes start with \_______ case.

lower,

upper

JTM (Java Virtual Machine)

A interpreter that reads bytecode and simulates its execution

Numeric Constants (Literals)

-What are the integer types?

byte, short, int, long

Numeric Constants (Literals)

-What are the floating-point types?

double, float

Character Constants

-letters and digits: 'A', 'B', 'C', ....

-punctuation symbols: '*', '\#', '$',..

-escape sequences

Escape Sequences

Allows us to include single/double quotes and other special characters

\" double quote

\' single quote

\\ backlash

\n start new line

\t tab character

int x \= 7;

int y \= 2;

x \= x/y;

System.out.print(x);

//What prints?

3 because 7/2 \= 3.5, however, x and y are integers, therefore the answer must also be an integer. Round the answer down to the nearest integer.

int x \= 7;

int y \= 2;

x \= x%y;

System.out.print(x);

//What prints?

1 because modulo (%) finds the remainder

Comparison Operators

-Equality/Inequality: \== or !\=

-Less than/Greater than: < or \>

-Less than or equal/Greater than or equal:

These return a boolean value true or false

String Concatenation

The '+' operator concatenates (joins) two strings

What happens when a string is concatenated with another type?

The other type is first evaluated and converted into its string representation and then joined

How do you compare strings?

string1.equals(string2)

string1.length()

string1.compareTo(string2)

What do you import if you want to use Scanner?

import java.util.Scanner;

How do you create a scanner object?

Scanner sc \= new Scanner(System.in);

int x;

//How do you set x to the user's inputted integer?

x \= sc.nextInt();

String x;

//How do you set x to the user's inputted string?

x \= sc.next();

Conditional Statements

if,

if-else

Logical Operator "and"

&&

Logical Operator "or"

||

Logical Operator "not"

!

What is the difference between Global variables and Local variables?

Global: scope is entire program

Local: scope is the block in which they are declared in

What does adding the special term "final" before a variable declaration do to the variable?

It makes the variable constant. If the variable value is attempted to be changed anywhere in the code it will result in an error.

What are the three loop types in Java?

while

do-while

for

What is one run through a loop called?

An iteration