2
Topics of theReview
• Essentials of object-oriented programming, in Java
• Java primitive data types, control structures, and arrays
• Using some predefined classes:
• Math
• JOptionPane, I/O streams
• String, StringBuffer, StringBuilder
• StringTokenizer
• Writing and documenting your own Java classes
3.
CSE 3
Some SalientCharacteristics of Java
• Java is platform independent: the same program can
run on any correctly implemented Java system
• Java is object-oriented:
• Structured in terms of classes, which group data with
operations on that data
• Can construct new classes by extending existing ones
• Java designed as
• A core language plus
• A rich collection of commonly available packages
• Java can be embedded in Web pages
4.
4
Java Processing andExecution
• Begin with Java source code in text files: Model.java
• A Java source code compiler produces Java byte code
• Outputs one file per class: Model.class
• May be standalone or part of an IDE
• A Java Virtual Machine loads and executes class files
• May compile them to native code (e.g., x86) internally
6
Classes and Objects
•The class is the unit of programming
• A Java program is a collection of classes
• Each class definition (usually) in its own .java file
• The file name must match the class name
• A class describes objects (instances)
• Describes their common characteristics: is a blueprint
• Thus all the instances have these same characteristics
• These characteristics are:
• Data fields for each object
• Methods (operations) that do work on the objects
7.
7
Grouping Classes: TheJava API
• API = Application Programming Interface
• Java = small core + extensive collection of packages
• A package consists of some related Java classes:
• Swing: a GUI (graphical user interface) package
• AWT: Application Window Toolkit (more GUI)
• util: utility data structures (important to CS 187!)
• The import statement tells the compiler to make
available classes and methods of another package
• A main method indicates where to begin executing a
class (if it is designed to be run as a program)
8.
8
A Little Exampleof import and main
import javax.swing.*;
// all classes from javax.swing
public class HelloWorld { // starts a class
public static void main (String[] args) {
// starts a main method
// in: array of String; out: none (void)
}
}
• public = can be seen from any package
• static = not “part of” an object
9.
9
Processing and RunningHelloWorld
• javac HelloWorld.java
• Produces HelloWorld.class (byte code)
• java HelloWorld
• Starts the JVM and runs the main method
10.
10
References and PrimitiveData Types
• Java distinguishes two kinds of entities
• Primitive types
• Objects
• Primitive-type data is stored in primitive-type variables
• Reference variables store the address of an object
• No notion of “object (physically) in the stack”
• No notion of “object (physically) within an object”
11.
11
Primitive Data Types
•Represent numbers, characters, boolean values
• Integers: byte, short, int, and long
• Real numbers: float and double
• Characters: char
12.
12
Primitive Data Types
Datatype Range of values
byte -128 .. 127 (8 bits)
short -32,768 .. 32,767 (16 bits)
int -2,147,483,648 .. 2,147,483,647 (32 bits)
long -9,223,372,036,854,775,808 .. ... (64 bits)
float +/-10-38
to +/-10+38
and 0, about 6 digits precision
double +/-10-308
to +/-10+308
and 0, about 15 digits precision
char Unicode characters (generally 16 bits per char)
boolean True or false
16
Type Compatibility andConversion
• Widening conversion:
• In operations on mixed-type operands, the numeric
type of the smaller range is converted to the numeric
type of the larger range
• In an assignment, a numeric type of smaller range
can be assigned to a numeric type of larger range
• byte to short to int to long
• int kind to float to double
17.
17
Declaring and SettingVariables
• int square;
square = n * n;
• double cube = n * (double)square;
• Can generally declare local variables where they are
initialized
• All variables get a safe initial value anyway (zero/null)
18.
18
Referencing and CreatingObjects
• You can declare reference variables
• They reference objects of specified types
• Two reference variables can reference the same object
• The new operator creates an instance of a class
• A constructor executes when a new object is created
• Example: String greeting = ″hello″;
19.
19
Java Control Statements
•A group of statements executed in order is written
• { stmt1; stmt2; ...; stmtN; }
• The statements execute in the order 1, 2, ..., N
• Control statements alter this sequential flow of execution
22
Methods
• A Javamethod defines a group of statements as
performing a particular operation
• static indicates a static or class method
• A method that is not static is an instance method
• All method arguments are call-by-value
• Primitive type: value is passed to the method
• Method may modify local copy but will not affect
caller’s value
• Object reference: address of object is passed
• Change to reference variable does not affect caller
• But operations can affect the object, visible to caller
24
Escape Sequences
• Anescape sequence is a sequence of two characters
beginning with the character
• A way to represents special characters/symbols
25.
25
The String Class
•The String class defines a data type that is used to
store a sequence of characters
• You cannot modify a String object
• If you attempt to do so, Java will create a new object
that contains the modified character sequence
26.
26
Comparing Objects
• Youcan’t use the relational or equality operators to
compare the values stored in strings (or other objects)
(You will compare the pointers, not the objects!)
27.
27
The StringBuffer Class
•Stores character sequences
• Unlike a String object, you can change the contents of
a StringBuffer object
29
Wrapper Classes forPrimitive Types
• Sometimes we need to process primitive-type data as
objects
• Java provides a set of classes called wrapper classes
whose objects contain primitive-type values: Float,
Double, Integer, Boolean, Character, etc.
30.
30
Defining Your OwnClasses
• Unified Modeling Language (UML) is a standard diagram
notation for describing a class
Class
name
Field
values
Class
name
Field
signatures:
type and name
Method signatures:
name, argument
types, result type
31.
31
Defining Your OwnClasses (continued)
• The modifier private limits access to just this class
• Only class members with public visibility can be
accessed outside of the class* (* but see protected)
• Constructors initialize the data fields of an instance
32.
32
The Person Class
//we have omitted javadoc to save space
public class Person {
private String givenName;
private String familyName;
private String IDNumber;
private int birthYear;
private static final int VOTE_AGE = 18;
private static final int SENIOR_AGE = 65;
...
33.
33
The Person Class(2)
// constructors: fill in new objects
public Person(String first, String family,
String ID, int birth) {
this.givenName = first;
this.familyName = family;
this.IDNumber = ID;
this.birthYear = birth;
}
public Person (String ID) {
this.IDNumber = ID;
}
34.
34
The Person Class(3)
// modifier and accessor for givenName
public void setGivenName (String given) {
this.givenName = given;
}
public String getGivenName () {
return this.givenName;
}
35.
35
The Person Class(4)
// more interesting methods ...
public int age (int inYear) {
return inYear – birthYear;
}
public boolean canVote (int inYear) {
int theAge = age(inYear);
return theAge >= VOTE_AGE;
}
36.
36
The Person Class(5)
// “printing” a Person
public String toString () {
return “Given name: “ + givenName + “n”
+ “Family name: “ + familyName + “n”
+ “ID number: “ + IDNumber + “n”
+ “Year of birth: “ + birthYear + “
n”;
}
37.
37
The Person Class(6)
// same Person?
public boolean equals (Person per) {
return (per == null) ? false :
this.IDNumber.equals(per.IDNumber);
}
38.
38
Arrays
• In Java,an array is also an object
• The elements are indexes and are referenced using the
form arrayvar[subscript]
39.
39
Array Example
float grades[]= new float[numStudents];
... grades[student] = something; ...
float total = 0.0;
for (int i = 0; i < grades.length; ++i) {
total += grades[i];
}
System.out.printf(“Average = %6.2f%n”,
total / numStudents);
40.
40
Array Example Variations
//possibly more efficient
for (int i = grades.length; --i >= 0; ) {
total += grades[i];
}
// uses Java 5.0 “for each” looping
for (float grade : grades) {
total += grade;
}
41.
41
Input/Output using ClassJOptionPane
• Java 1.2 and higher provide class JOptionPane, which
facilitates display
• Dialog windows for input
• Message windows for output
43
Converting Numeric Stringsto Numbers
• A dialog window always returns a reference to a String
• Therefore, a conversion is required, using static
methods of class String:
44.
44
Input/Output using Streams
•An InputStream is a sequence of characters
representing program input data
• An OutputStream is a sequence of characters
representing program output
• The console keyboard stream is System.in
• The console window is associated with System.out
45.
45
Opening and UsingFiles: Reading Input
import java.io.*;
public static void main (String[] args) {
// open an input stream (**exceptions!)
BufferedReader rdr =
new BufferedReader(
new FileReader(args[0]));
// read a line of input
String line = rdr.readLine();
// see if at end of file
if (line == null) { ... }
46.
46
Opening and UsingFiles: Reading Input (2)
// using input with StringTokenizer
StringTokenizer sTok =
new StringTokenizer (line);
while (sTok.hasMoreElements()) {
String token = sTok.nextToken();
...;
}
// when done, always close a stream/reader
rdr.close();
47.
47
Alternate Ways toSplit a String
• Use the split method of String:
String[] = s.split(“s”);
// see class Pattern in java.util.regex
• Use a StreamTokenizer (in java.io)
48.
48
Opening and UsingFiles: Writing Output
// open a print stream (**exceptions!)
PrintStream ps = new PrintStream(args[0]);
// ways to write output
ps.print(“Hello”); // a string
ps.print(i+3); // an integer
ps.println(“ and goodbye.”); // with NL
ps.printf(“%2d %12d%n”, i, 1<<i); // like C
ps.format(“%2d %12d%n”, i, 1<<i); // same
// closing output streams is very important!
ps.close();
49.
49
Summary of theReview
• A Java program is a collection of classes
• The JVM approach enables a Java program written on
one machine to execute on any other machine that has a
JVM
• Java defines a set of primitive data types that are used
to represent numbers, characters, and boolean data
• The control structures of Java are similar to those found
in other languages
• The Java String and StringBuffer classes are used
to reference objects that store character strings
50.
50
Chapter Review (continued)
•Be sure to use methods such as equals and
compareTo to compare the contents of String objects
• You can declare your own Java classes and create
objects of these classes using the new operator
• A class has data fields and instance methods
• Array variables can reference array objects
• Class JOptionPane can be used to display dialog
windows for data entry and message windows for output
• The stream classes in package java.io read strings
from the console and display strings to the console, and
also support file I/O
![8
A Little Example of import and main
import javax.swing.*;
// all classes from javax.swing
public class HelloWorld { // starts a class
public static void main (String[] args) {
// starts a main method
// in: array of String; out: none (void)
}
}
• public = can be seen from any package
• static = not “part of” an object](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/85/Introduction-to-Java-basic-understanding-ppt-8-320.jpg)
![14
Operators
1. subscript [ ], call ( ), member access .
2. pre/post-increment ++ --, boolean complement !,
bitwise complement ~, unary + -, type cast (type),
object creation new
3. * / %
4. binary + - (+ also concatenates strings)
5. signed shift << >>, unsigned shift >>>
6. comparison < <= > >=, class test instanceof
7. equality comparison == !=
8. bitwise and &
9. bitwise or |](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/85/Introduction-to-Java-basic-understanding-ppt-14-320.jpg)
![38
Arrays
• In Java, an array is also an object
• The elements are indexes and are referenced using the
form arrayvar[subscript]](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/85/Introduction-to-Java-basic-understanding-ppt-38-320.jpg)
![39
Array Example
float grades[] = new float[numStudents];
... grades[student] = something; ...
float total = 0.0;
for (int i = 0; i < grades.length; ++i) {
total += grades[i];
}
System.out.printf(“Average = %6.2f%n”,
total / numStudents);](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/85/Introduction-to-Java-basic-understanding-ppt-39-320.jpg)
![40
Array Example Variations
// possibly more efficient
for (int i = grades.length; --i >= 0; ) {
total += grades[i];
}
// uses Java 5.0 “for each” looping
for (float grade : grades) {
total += grade;
}](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/85/Introduction-to-Java-basic-understanding-ppt-40-320.jpg)
![45
Opening and Using Files: Reading Input
import java.io.*;
public static void main (String[] args) {
// open an input stream (**exceptions!)
BufferedReader rdr =
new BufferedReader(
new FileReader(args[0]));
// read a line of input
String line = rdr.readLine();
// see if at end of file
if (line == null) { ... }](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/85/Introduction-to-Java-basic-understanding-ppt-45-320.jpg)
![47
Alternate Ways to Split a String
• Use the split method of String:
String[] = s.split(“s”);
// see class Pattern in java.util.regex
• Use a StreamTokenizer (in java.io)](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/85/Introduction-to-Java-basic-understanding-ppt-47-320.jpg)
![48
Opening and Using Files: Writing Output
// open a print stream (**exceptions!)
PrintStream ps = new PrintStream(args[0]);
// ways to write output
ps.print(“Hello”); // a string
ps.print(i+3); // an integer
ps.println(“ and goodbye.”); // with NL
ps.printf(“%2d %12d%n”, i, 1<<i); // like C
ps.format(“%2d %12d%n”, i, 1<<i); // same
// closing output streams is very important!
ps.close();](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/85/Introduction-to-Java-basic-understanding-ppt-48-320.jpg)
![8
A Little Example of import and main
import javax.swing.*;
// all classes from javax.swing
public class HelloWorld { // starts a class
public static void main (String[] args) {
// starts a main method
// in: array of String; out: none (void)
}
}
• public = can be seen from any package
• static = not “part of” an object](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/75/Introduction-to-Java-basic-understanding-ppt-8-2048.jpg)
![14
Operators
1. subscript [ ], call ( ), member access .
2. pre/post-increment ++ --, boolean complement !,
bitwise complement ~, unary + -, type cast (type),
object creation new
3. * / %
4. binary + - (+ also concatenates strings)
5. signed shift << >>, unsigned shift >>>
6. comparison < <= > >=, class test instanceof
7. equality comparison == !=
8. bitwise and &
9. bitwise or |](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/75/Introduction-to-Java-basic-understanding-ppt-14-2048.jpg)
![38
Arrays
• In Java, an array is also an object
• The elements are indexes and are referenced using the
form arrayvar[subscript]](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/75/Introduction-to-Java-basic-understanding-ppt-38-2048.jpg)
![39
Array Example
float grades[] = new float[numStudents];
... grades[student] = something; ...
float total = 0.0;
for (int i = 0; i < grades.length; ++i) {
total += grades[i];
}
System.out.printf(“Average = %6.2f%n”,
total / numStudents);](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/75/Introduction-to-Java-basic-understanding-ppt-39-2048.jpg)
![40
Array Example Variations
// possibly more efficient
for (int i = grades.length; --i >= 0; ) {
total += grades[i];
}
// uses Java 5.0 “for each” looping
for (float grade : grades) {
total += grade;
}](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/75/Introduction-to-Java-basic-understanding-ppt-40-2048.jpg)
![45
Opening and Using Files: Reading Input
import java.io.*;
public static void main (String[] args) {
// open an input stream (**exceptions!)
BufferedReader rdr =
new BufferedReader(
new FileReader(args[0]));
// read a line of input
String line = rdr.readLine();
// see if at end of file
if (line == null) { ... }](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/75/Introduction-to-Java-basic-understanding-ppt-45-2048.jpg)
![47
Alternate Ways to Split a String
• Use the split method of String:
String[] = s.split(“s”);
// see class Pattern in java.util.regex
• Use a StreamTokenizer (in java.io)](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/75/Introduction-to-Java-basic-understanding-ppt-47-2048.jpg)
![48
Opening and Using Files: Writing Output
// open a print stream (**exceptions!)
PrintStream ps = new PrintStream(args[0]);
// ways to write output
ps.print(“Hello”); // a string
ps.print(i+3); // an integer
ps.println(“ and goodbye.”); // with NL
ps.printf(“%2d %12d%n”, i, 1<<i); // like C
ps.format(“%2d %12d%n”, i, 1<<i); // same
// closing output streams is very important!
ps.close();](https://image.slidesharecdn.com/introductiontojava-250807091600-9cd7dea2/75/Introduction-to-Java-basic-understanding-ppt-48-2048.jpg)
