Home Java JavaBase what is collection java

what is collection java

Nov 11, 2019 am 09:17 AM
java gather

what is collection java

What is collection java

1. The origin of collection

Usually, our Java program needs to know how many objects are created when the program is running. But if the program is not running, during the program development stage, we have no idea how many objects are needed, or even their exact type. In order to meet these general programming needs, we require that any number of objects can be created at any time and anywhere. What are these objects used to accommodate? We thought of arrays first, but! Arrays can only store data of the same type, and their length is fixed, so what should we do? The collection came into being. ( Recommended tutorial: java tutorial )

2. What is a collection?

The Java collection class is stored in the java.util package, is a container used to store objects.

Note:

1. Collections can only store objects. For example, if you store an int type data 66 into a collection, it is actually converted into an Integer class and then stored automatically. Each basic data type in Java has a corresponding reference type.

2. Collections store references to objects, not the objects themselves. So we call the objects in the collection the references to the objects in the collection. The object itself is still placed in the heap memory.

3. Collections can store different types of data types, with no limit on the number.

3. Collections in Java are mainly divided into four categories:

● List list, ordered, repeatable

● Queue queue, with Ordered, repeatable

● Set collection, non-repeatable

● Map mapping, unordered, unique keys, non-unique values ​​Each collection type contains multiple specific implementation classes

The above is the detailed content of what is collection java. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undress AI Tool

Undress AI Tool

Undress images for free

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Hot Topics

PHP Tutorial
1596
276
What is a deadlock in Java and how can you prevent it? What is a deadlock in Java and how can you prevent it? Aug 23, 2025 pm 12:55 PM

AdeadlockinJavaoccurswhentwoormorethreadsareblockedforever,eachwaitingforaresourceheldbytheother,typicallyduetocircularwaitcausedbyinconsistentlockordering;thiscanbepreventedbybreakingoneofthefournecessaryconditions—mutualexclusion,holdandwait,nopree

You are not currently using a display attached to an NVIDIA GPU [Fixed] You are not currently using a display attached to an NVIDIA GPU [Fixed] Aug 19, 2025 am 12:12 AM

Ifyousee"YouarenotusingadisplayattachedtoanNVIDIAGPU,"ensureyourmonitorisconnectedtotheNVIDIAGPUport,configuredisplaysettingsinNVIDIAControlPanel,updatedriversusingDDUandcleaninstall,andsettheprimaryGPUtodiscreteinBIOS/UEFI.Restartaftereach

How to use Optional in Java? How to use Optional in Java? Aug 22, 2025 am 10:27 AM

UseOptional.empty(),Optional.of(),andOptional.ofNullable()tocreateOptionalinstancesdependingonwhetherthevalueisabsent,non-null,orpossiblynull.2.CheckforvaluessafelyusingisPresent()orpreferablyifPresent()toavoiddirectnullchecks.3.Providedefaultswithor

PS oil paint filter greyed out fix PS oil paint filter greyed out fix Aug 18, 2025 am 01:25 AM

TheOilPaintfilterinPhotoshopisgreyedoutusuallybecauseofincompatibledocumentmodeorlayertype;ensureyou'reusingPhotoshopCS6orlaterinthefulldesktopversion,confirmtheimageisin8-bitperchannelandRGBcolormodebycheckingImage>Mode,andmakesureapixel-basedlay

Java Cryptography Architecture (JCA) for Secure Coding Java Cryptography Architecture (JCA) for Secure Coding Aug 23, 2025 pm 01:20 PM

Understand JCA core components such as MessageDigest, Cipher, KeyGenerator, SecureRandom, Signature, KeyStore, etc., which implement algorithms through the provider mechanism; 2. Use strong algorithms and parameters such as SHA-256/SHA-512, AES (256-bit key, GCM mode), RSA (2048-bit or above) and SecureRandom; 3. Avoid hard-coded keys, use KeyStore to manage keys, and generate keys through securely derived passwords such as PBKDF2; 4. Disable ECB mode, adopt authentication encryption modes such as GCM, use unique random IVs for each encryption, and clear sensitive ones in time

Building Cloud-Native Java Applications with Micronaut Building Cloud-Native Java Applications with Micronaut Aug 20, 2025 am 01:53 AM

Micronautisidealforbuildingcloud-nativeJavaapplicationsduetoitslowmemoryfootprint,faststartuptimes,andcompile-timedependencyinjection,makingitsuperiortotraditionalframeworkslikeSpringBootformicroservices,containers,andserverlessenvironments.1.Microna

Java Persistence with Spring Data JPA and Hibernate Java Persistence with Spring Data JPA and Hibernate Aug 22, 2025 am 07:52 AM

The core of SpringDataJPA and Hibernate working together is: 1. JPA is the specification and Hibernate is the implementation, SpringDataJPA encapsulation simplifies DAO development; 2. Entity classes map database structures through @Entity, @Id, @Column, etc.; 3. Repository interface inherits JpaRepository to automatically implement CRUD and named query methods; 4. Complex queries use @Query annotation to support JPQL or native SQL; 5. In SpringBoot, integration is completed by adding starter dependencies and configuring data sources and JPA attributes; 6. Transactions are made by @Transactiona

Fixed: Windows Is Showing 'A required privilege is not held by the client' Fixed: Windows Is Showing 'A required privilege is not held by the client' Aug 20, 2025 pm 12:02 PM

RuntheapplicationorcommandasAdministratorbyright-clickingandselecting"Runasadministrator"toensureelevatedprivilegesaregranted.2.CheckUserAccountControl(UAC)settingsbysearchingforUACintheStartmenuandsettingtheslidertothedefaultlevel(secondfr

See all articles