session4 module5-6 array string package accessmodifiers

7/28/2019 Session4 Module5-6 Array String Package AccessModifiers

1/25

Session 4

Module 5: Arrays/Strings/Otherstring classes

Module 6: Packages , Access

Modifiers


2/25

Arrays & String / Package & Modifiers / Session4 / 2 of 25

Module 4 - Review

Class = data + methods

Object = an instance of a class

Instance variable: a variable contains a reference toan object.

Method: a behavior of a class (code)

Constructor: a method which is executed when anobject is created.

Initializer: Codes which will be executed just after anobject is created to set the initial values to data ofobject.


3/25


Module 5 Objectives

Arrays

String

StringBuilder StringTokenizer


4/25


Definition

An array is a special data store that can hold several

items of a single data type in contiguous memory

locations.

Benefits Arrays are the best means of operating on multiple data

elements of the same type at the same time.

Arrays make optimum use of memory resource as

compared to variables. Memory can be assigned to an array only at the time when

the array is actually used.


5/25


Declaring:

Type[][] m;// or Type m[][];

Allocating memory:

m = new Type[RowNo][ColNo];

Element accessing:

m[r_index][c_index] // index >= 0

Traversing a 2D array(Type[][] m)

for (int i=0; i


6/25


String class

Class forimmutable text data.

Strings are constant, which means

their values cannot be changed after

they are created. Declare:

String S1 = new String();

String s2 = "Hello";

S2

1000

e

l

l

o

H

1000

(in java.lang package)


7/25


String class

Common-used methods (1)


8/25


String class

Common-used methods (2)


9/25


String Arrays

String[] list = { "EPC", "HDJ",

"DWMX", "SQL",};

for (int i=0;i< list.length;i++)

System.out.println(list[i]);

HDJ

EPC

DWMX

SQL

list

2000

4000

5000

3000

1000

3000

2000

4000

5000

1000


10/25


Passing command line

arguments

classA{ ..

publicstaticvoid main (String[] args){

// manipulate with args[i]

}}

// run program

java A arg0 arg1 arg2


11/25


StringBuilder classStore a growable and flexible string.

Characters or strings can be inserted in the stringBuilder object and they

can also be appended at the end.

Constructors

(in java.lang package)


12/25


StringBuilder class

Common-used methods


13/25


StringTokenizer class Class for break a string (tokenizer function) into subunits (called tokens)

based on a specific delimiter. The most common delimiter is whitespace which yields words as the

tokens.

Tom persues JerryTom

persues

Jerry

delimiter = " "

subunits(called tokens)

break a string

(tokenizer function)

(in java.util package)


14/25


StringTokenizer class

Common-used methods


15/25


Module 6 - Objectives

Packages

Access Modifiers

Field and method Modifiers


16/25



17/25


Predefined Packages

You can view its

content with

WINZAR/ WINZIP

importjava.util.*;importjava.io.*;

class A

{

}


18/25


User-defined Packages

Create a packagepackage my_package;

class A {

.

} Use the package

import my_package.A;

class B{

.

void method3() {A obj = new A();

..

}

}

fully qualified name of the class(the name of the class including

its package name.)

must be the first line


19/25


Access Modifiers

Access specifiers (modifiers) are used to control the

access of classes and class members.

The access specifiers also determine whether

classes and the members of the classes can beinvoked by other classes or interfaces.

Accessibility affects inheritance and how members

are inherited by the subclass.


20/25


Access control keyword

public

protected

private

no specifier

(default

or package)

interface

class

member of

interface/class

Free-accessing

(even outside its package)

package/class/ subclass

outside cannot access

(only within its own class)

package

Access level Applied tokeywords


21/25


Rules for access control

Constructor is a special method, so it is certainly a member of class


22/25


Access control keywords

Access

modifier

Elements Visible in

Class Package Subclass Outside

package

public yes yes yes yes

protected yes yes yes no

private yes no no no

no modifier yes yes no no


23/25


Field and method Modifiers

Keywords for specifying changing permission

volatile(dbini) modifier (applied only to fields) Allows the content of a variable to be synchronized across all running

threads. This modifier is not frequently used

final(cui cng) modifier

native(ccb) modifier Used only with methods and indicates that the implementation of the method

is in a language other than in Java.

transient(tmthi) modifier Is used to declare fields that are not saved or restored as a part of the state

of the object.


24/25


Rules for using Fields and

Methods modifier


25/25


Module 5, 6 - Summary

Arrays

String

StringBuilder StringTokenizer

Packages

Access Modifiers

Field and methodModifiers

session4 module5-6 array string package accessmodifiers

Documents