Download Computers, Programs, and Java What is a Computer? Computer

Computer: Central Processing Unit (CPU)
Computers, Programs, and Java
• Retrieves instructions (from memory)
and executes them
• Built on a small silicon semiconductor
chip that contains millions of transistors
(tiny electric switches) for processing
information.
CSE114: Computer Science I
Spring 2017
• Multiple parts (i.e., cores) that read and
C HEN -W EI WANG
execute instructions independently.
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What is a Computer?
Computer: Storing Information
Bus
Storage
Devices
Memory
CPU
e.g., Disk, CD,
and Tape
• A computer is really a series of switches: each switch can be in
Communication
Devices
Input
Devices
Output
Devices
e.g., Modem,
and NIC
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
A computer includes both:
• Hardware
visible, physical, tangible (peripheral) devices
repeatedly and efficiently executes given instructions
• Software
invisible, abstract, intangible task-control instructions
reflects programmers’ intelligence
Does the notion of stupid computer really make sense?
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an on state or an off state.
• The possible states of a switch are called a bit.
• Information is stored as data by being encoded into a sequence
of on-off switches.
Q. # of possibilities that can be stored in n bits (n 1)?
2n
Q. # of bits required to store n data items (n > 0)?
dlog2 ne
Data of various kinds, e.g., numbers and characters, are encoded
as a series of bits.
As a programmer, you need not worry about the encoding scheme.
e.g., In an ASCII Table, we use 7 bits to encode 128 characters.
• Basic unit of computer storage is a byte (equivalent to 8 bits).
Kilobyte (KB); Megabyte (MB); Gigabyte (GB); Terabyte (TB)
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Computer: Memory Illustrated
Memory address
Memory content
.
.
.
.
.
.
2000
01001010
Encoding for character ‘J’
2001
01100001
Encoding for character ‘a’
2002
01110110
Encoding for character ‘v’
2003
01100001
Encoding for character ‘a’
2004
00000011
Encoding for number 3
Programming Languages (1)
• What computers read is difficult for humans, and vice versa.
Computers are good at processing machine language (0s and 1s).
Human beings are good at abstract thinking for problem solving.
• Assembly language is a big step forward for humans to specify
steps of primitive instructions (e.g., memory loads/stores,
arithmetic operations, etc.).
Say $t0, $t1, $t2, $n, $i are addresses; $n stores value N:
lw
mult
lw
mult
add
sw
$t0,
$t0,
$t1,
$t1,
$t2,
$t2,
$n
$t0, $t0
$n
$t1, 3
$t0, $t1
$i
#
#
#
#
#
#
fetch
store
fetch
store
store
store
N, store in $t0
N*N in $t0
N, store in $t1
3*N in $t1
N*N + 3*N in $t2
N*N + 3*N in $i
Level of abstraction of the assembly is still too low for humans.
The above is equivalent to a line of Java code: i = N*N + 3*N
You will have fun with programming in assembly code in CSE220!
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.
.
.
.
.
Computer: Memory
Programming Languages (2)
• Like the CPU, memory is built on a silicon semiconductor chip.
• A computer’s memory consists of an ordered sequence of
• High-level programming language (e.g., Java) is even closer
bytes for storing
programs;
data that the program works with.
• A computer’s work area for executing a program
Data may have to be loaded from external storage devices.
Every byte in the memory has a unique address.
• A computer’s memory is volatile: when the system’s power is
to our natural way of thinking (i.e., closer to “writing an essay”).
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2
3
4
5
Scanner keyboard = new Scanner(System.in);
int weight = keyboard.nextInt();
int height = keyboard.nextInt();
int bmi = weight / (height * height);
System.out.println("BMI (Body Mass Index) is: " + bmi);
turned off, all information stored is lost.
Need external storage devices for permanent storage.
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Operating Systems
Java Language Specification and API
• When writing Java programs, you must follow the predefined
• Each operating system is still a computer program.
• Executing it regulates other programs by properly allocating
resources of your computer (i.e., CPU and memory).
• You will learn about OS in CSE306.
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Why Java?
Java enables users to develop and deploy applications on:
• Internet servers
• desktop computers
• small hand-held devices
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syntax; otherwise, it cannot be compiled into machine code
for the computer to execute.
• Java syntax is defined int he Java language specification:
https://docs.oracle.com/javase/specs/.
• Programming interface for Java applications is defined in the
Java API:
http://docs.oracle.com/javase/8/docs/api/.
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Compile Time vs. Runtime
• These terms refer to two stages of developing your program.
• Compile time:
Period where you type/compile Java code in the Eclipse editor.
• Runtime:
Period which occurs after you run/execute you Java code.
For a piece of Java code to be executed, it must not contain any
compile-time errors.
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A Simple Java Program
Beyond this lecture. . .
public class Welcome {
public static void main(String[] args) {
/* Print a greeting message to the console. */
System.out.println("Welcome to Java!");
}
}
• main method: Entry point for the program execution
• 3 different categories of errors:
Compile time errors:
• syntax error
• type errors
• Read Chapter 1 in the textbook.
• Install Eclipse and try out the simple examples in Chapter 1.
[e.g., writing 2 #$# 3]
[e.g., writing "2" + 3]
Runtime errors:
• programs terminate abnormally
[e.g., executing 10/0]
Logical errors:
• programs terminate normally but the results are wrong
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[e.g., calculating (pi ⇤ r )(pi ⇤ r ) for the area of a circle of radius r]
Developing Java Programs
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Index (1)
What is a Computer
Computer: Central Processing Unit (CPU)
Computer: Storing Information
Computer: Memory Illustrated
Computer: Memory
Programming Languages (1)
Programming Languages (2)
Operating Systems
Why Java?
Java Language Specification and API
Compile Time vs. Runtime
A Simple Java Program
Developing Java Programs
Beyond this lecture. . .
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