Comprog2 Flashcards
java history
- created by James Gosling
- green team
- green project
- in 1991 (Sun Microsystems)
- initially called “oak” (in honor for the tree outside Gosling’s window)
java characteristics
simple
object-oriented
distributed
architecture neutral
portable
high-performance
interpreted
robust
secure
multi-threaded
dynamic
program’s source file?
compile-time environment
program’s class file?
run-time environment
parts of Java’s simple code
multi-line comment
package name
class header
main method
program body
simple code interpretation
/*
*
*/
package unes;
public class Unes {
public static void main (String [ ] args) {
System.out.println(“Hi”);
}
}
what is a variable?
an item of data used to store state of objects
a variable has?
a data type and a name
these are case-sensitive
variable names
it may be letters, digits, dollar signs, or underscore characters
subsequent characters
if the name you choose consists of only one word, spell that word in?
all lowercase letters
java primitive data types
logical - Boolean
textual - char
integral - byte, short, int, and long
floating point - float and double
they represent simple values that have built-in functionality in the language
primitive data types
they represent simple values such as numbers, Booleans, and characters
primitive data types
name of place in memory that can contain data
variable
kind of data variable can contain
data type
identifier that refers to the variable
name
the default or specified value
value
also called the literal of the statement
value
all Java statements end with a?
semicolon ;
how to declare a variable?
data type name;
int grade;
double ave1, ave2;
boolean isVerified;
= is called?
an assignment operator
== is called?
a comparative equals
if variable is not initialized, most will default to ____. All variables should be initialized
null
operators in java
arithmetic operators
relational operators
logical operators
assignment operators
string operator
used in mathematical expressions in the same way that they are used in algebra
arithmetic operators
used to concatenate any number of strings, on either side of the string
+ operator
link (things) together in a chain or series
concatenate
create a code that will have an output:
I am Michelle Eunice
1 public class concatStr {
2 public static void main(String[] args) {
3 String n1 = “Michelle”;
4 String n2 = “Eunice”;
5 String name = n1 + “ ” + n2;
6 System.out.println(“I am ” + name);
7 }
8 }
used to decrement/increment variable value by 1 after assigning the value to the variable
post decrement/increment operator
used to decrement/increment variable value by 1 before assigning the value to the variable
pre decrement/increment operator
a character preceded by a backslash () and has a special meaning to the compiler
escape sequence
insert a tab
\t
insert a backspace
\b
insert a newline
\n
insert a carriage return
\r
insert a form feed
\f
insert a single quote character
'
insert a double quote character
"
insert a backslash character
\
errors in java
syntax error
run time error
semantic error
also called compile time error
syntax error
these are errors where the compiler finds something wrong with your program, and you can’t even try to execute it
syntax error
detected during the execution of the program
run time error
occur when a program does not contain any syntax errors but asks the computer to do something that the computer is unable to reliably do
run time error
also called logic error
semantic error
happens when your program compiles and executes, but does the wrong thing or returns an incorrect result or no output when it should be returning an output
semantic error
caused by an incorrect idea or concept used by a programmer while coding
semantic error
you must put this to help you figure out what the program is actually doing
print statements
you must use this to step through your program and watch what it does
debugger
it is similar to decision-making in real life
decision-making in programming
uses control statements to control the flow of execution of program based on certain conditions
programming language
java’s selection statements
if
if-else
if-else-if
nested-if
switch-case
jump – break, continue, return
the most simple decision making statement. It is used to decide whether a certain statement or block of statements will be executed or not
if statement
an optional companion to the if statement that can extend its usefulness
else statement
a user can decide among multiple options
if-else-if ladder statement
the statement executed as a result of an if statement or else clause could be another if statement
nested if statements
it does not determine which if and else matches with, it is determined by the curly brackets
indentation
provides another way to decide which statement to execute next
switch statement
used as the last statement in each case’s statement list
break statement
it is a reserved word in Java
break
causes control to transfer to the end of the switch statement
break statement
a switch statement can have an optional ____?
default case
it has no associated value and simply uses the reserved word default
default case
though it can be positioned anywhere in the switch statement, it is usually placed at the end
default case
