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java.util.ArrayList

(Later we will see another way to accomplish this that requires less typing effort.)

The exception

The one exception to the rule is the use of classes in the java.lang package, (such as Boolean , Class , and Double ) . Your source code can refer to classes in the java.lang package without the requirement to provide a fully-qualified class name.

An ArrayList object

Now back to the use of the object previously instantiated from the class named ArrayList . This is the kind of object that is often referred to as a container.

(A container in this sense is an object that is used to store references to other objects.)

Many methods available

An object of the ArrayList class provides a variety of methods that can be used to store object references and to fetch the references that it contains.

The add method

One of those methods is the method named add .

The following code fragment instantiates three objects of the String class, and stores them in the ArrayList object instantiated earlier.

(Note that since the initial capacity of the ArrayList object was adequate to store only a single reference, the following code causes the object toautomatically increase its capacity to at least three.)

ref.add("ABC "); ref.add("DEF ");ref.add("GHI");

The get() method

The references stored in an object of the ArrayList class can be fetched by calling the get method on a reference to the object passing a parameter of type int .

The code in the following fragment calls the get method to fetch the references stored in index locations 0, 1, and 2. These references are passed to the println method, where the contents of the String objects referred to by those references are concatenated and displayed on the computerscreen.

System.out.println( (String)ref.get(0) +(String)ref.get(1) + (String)ref.get(2));

The output

This results in the following being displayed:

ABC DEF GHI

Summary

The above discussion gave you a preview into the use of containers in general, and the ArrayList container in particular.

However, the primary purpose of this program was to help you to understand the use of packages in Java.

The ArrayList class was simply used as an example of a class file that is stored in a standard Java package.

Back to Question 3

Answer 2

D. Joe Joe true

Explanation 2

Two String objects with identical contents

As in Question 1 , the program instantiates two String objects containing identical character strings, as shown in the following codefragment.

char[] anArray = {'J','o','e'};String Str1 = new String(anArray); String Str2 = new String(anArray);

Compare objects for equality

Also, as in Question 1 , this program compares the two objects for equality and displays the result as shown by the call to the equals method in the following fragment.

System.out.println( Str1 + " " + Str2 + " " +Str1.equals(Str2));

Compare using overridden equals method

The == operator is not used to compare the two objects in this program. Instead, the objects are compared using an overridden version of the equals method. In this case, the equals method returns true, indicating that the objects are of the same type and contain thesame data values.

Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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