Java程序辅导

Introductory Programming In Java
Comp6700/Comp2140
Week 2, 2016
Henry Gardner/ Alexei Khorev/ Charles Martin
Please be aware that this course moves fast.
Some of you may need to spend more time on lab and 
homework exercises than others.
Some of you may need to read widely (web, textbooks, etc) 
to catch up.
We provide you with a lot of material as a starting point.
Some in lectures
More in lecture notes
More in lecturettes etc
Remember that Introductory Programming in Java is a 
“messy” subject and that core concepts are interlinked. We 
will continue to reinforce core concepts as the course 
proceeds.
How are you coping……?
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From 2015, ANU introduced what computer 
science interprets as a “no extensions” policy for 
work submitted for assessment during the 
semester:
Extensions are only to be granted for reasons such as 
illness or personal/family difficulties.
Reasons need to be documented and a formal 
application needs to be made.
Computer Science cannot allow late submissions with 
a marks penalty.
Important note on assessment
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Some CS courses allow all continuous marks to be 
redeemed on the final examination.
We propose that COMP6700/COMP2140 follow this 
pattern
This will mean that if you do not submit homeworks, or 
the assignments, or the mid-semester exam, then your 
final exam marks will be normalised to cover these 
unsubmitted items.
To be fair, if students have submitted items and their scaled 
final exam mark is higher than the marks that they received for 
those items then they should receive the final mark.
But we can allow marks to be redeemed
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Presently:
Final mark =  HW (10)  + max(MSE1, MSE2*0.8) (10)  
+ asst1 (15) + asst2 (15) + Exam (50)
We propose
Final Mark = max(HW, Ex*0.2) (10) + max(MSE1, 
MSE2, Ex*0.2) (10) + max(asst1,Ex*0.3) (15) + 
max(asst2,Ex*0.3) (15) + Exam (50)
So deadlines will have no late extensions, but marks can 
be redeemed. The second mid-semester exam can redeem 
the first MSE to 100%.
Comments?
For COMP6700/COMP2140
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See Alexei’s J2 notes on the “FTA” (free-to-air) website
Identify types and literals in the following code:
J2 – Primitive data types and type conversion
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Some common literals: 
Java “literals”
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Every variable must be declared by specifying its type.
There are eight  primitive  types:
boolean (1-bit,  true/false)
byte (8-bit  signed,  range  -128 ... +127)
char (16-bit  unicode,  character symbols from Unicode Table)
short (16-bit  signed,  range  -32768 ... +32767)
int (32-bit  signed,  range  -2,147,483,648 ... +2,147,483,647)
long (64-bit  signed range  -9,223,372,036,854,775,808 ...
+9,223,372,036,854,775,807)
float (32-bit  FP  number)
double (64-bit  FP  number)
“int” and “double” are the default numerical types
Java is strongly typed
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Strings are sequences of characters (char)
You create and manipulate String objects!
https://docs.oracle.com/javase/8/docs/api/java/lang/String.html
String is not a primitive type
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Types have different lengths
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• Java can automatically convert between compatible types.
• (Where the type on the left hand side of an assignment 
statement is larger than the type on the right hand side)
• Sometimes java needs to be told to cast one type to another
• Syntax: var1 = (type1) var2; 
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Default behaviour of (int) is to truncate the decimal part.
Math.round, Math.ceil, Math.floor can be used to change 
this behaviour
Rounding and finite precision
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Some numbers can be tricky than they look 
because of binary representation
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You should use Math.round in situations like this where a long binary 
representation could be truncated to the wrong integer. 
See J2 notes on the char data type to represent single 
characters
“char” literal values have an order, like the 
sequencing of characters in the alphabet
Java uses Unicode character encoding: it can 
represent any character in any language in the world!
Strings are sequences of characters   
Characters
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An array  is an ordered  collection  of data  elements  
indexed from 0 (first element) up to length - 1.  All 
elements  have the  same  type. 
Array declarations and instantiations can be done in 
different ways. 
Note that you can use the “new” command to create 
arrays. “new” creates objects in Java. Java arrays are 
objects.
Arrays
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“A nightmare of epic proportions” – Cay Horstmann
Can use “args” array of Strings and convert to whatever 
primitive data type you require.
Can use “Scanner”
Can use “JOptionPane”
Can read from files, from databases, from web pages, 
from streams, from twitter, from …….
Getting information into your Java program
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Scanner
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Scanner….
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