Java generics mainly include "define generic classes", "define generic interfaces", "define generic methods", "instantiate generic classes or interfaces", "use wildcards" and "use generics". Six uses of "type qualification": 1. Define a generic class and use
to represent type parameters; 2. Define a generic interface and use to represent type parameters; 3. Define a generic method , use to represent type parameters; 4. When instantiating a generic class or interface, specify specific type parameters; 5. Use wildcards to represent a subtype or supertype of a certain generic type.
Java generics are mainly used in the following ways:
- Define generic classes
You can define a generic class, use
public?class?MyList<T>?{
????private?T[]?array;
????public?MyList(T[]?array)?{
????????this.array?=?array;
????}
????public?T?get(int?index)?{
????????return?array[index];
????}
}
- Define a generic interface
You can define a generic interface, use
public?interface?MyInterface<T>?{
????T?doSomething();
}
- Define a generic method
You can define a generic method, use
public?<T>?T?doSomething(T?param)?{
????//?...
}
- Instantiate a generic class or interface
When instantiating a generic class or interface, specific type parameters must be specified, for example:
MyList<String>?list?=?new?MyList<>(new?String[]{"a",?"b",?"c"});
- Use wildcards
You can use wildcards to represent subtypes or supertypes of a certain generic type, including ?, ? extends T and ? super T. , for example:
MyList<? extends Number>?list1?=?new?MyList<>(new?Integer[]{1,?2,?3});
MyList<? super Integer>?list2?=?new?MyList<>(new?Number[]{1.0,?2.0,?3.0});
Among them, list1 can accept any type that is a subtype of Number (such as Integer, Float, etc.) as an element, while list2 can accept any type that is a supertype of Integer (such as Number, Object, etc.) as elements.
- Using generic qualification
You can use generic qualification to limit the scope of type parameters, including extends and super, for example:
public?<T extends Number>?void?doSomething(T?param)?{
????//?...
}
Among them,
The above is the detailed content of How to use Java generics. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
VSCode settings.json location
Aug 01, 2025 am 06:12 AM
The settings.json file is located in the user-level or workspace-level path and is used to customize VSCode settings. 1. User-level path: Windows is C:\Users\\AppData\Roaming\Code\User\settings.json, macOS is /Users//Library/ApplicationSupport/Code/User/settings.json, Linux is /home//.config/Code/User/settings.json; 2. Workspace-level path: .vscode/settings in the project root directory
How to handle transactions in Java with JDBC?
Aug 02, 2025 pm 12:29 PM
To correctly handle JDBC transactions, you must first turn off the automatic commit mode, then perform multiple operations, and finally commit or rollback according to the results; 1. Call conn.setAutoCommit(false) to start the transaction; 2. Execute multiple SQL operations, such as INSERT and UPDATE; 3. Call conn.commit() if all operations are successful, and call conn.rollback() if an exception occurs to ensure data consistency; at the same time, try-with-resources should be used to manage resources, properly handle exceptions and close connections to avoid connection leakage; in addition, it is recommended to use connection pools and set save points to achieve partial rollback, and keep transactions as short as possible to improve performance.
python itertools combinations example
Jul 31, 2025 am 09:53 AM
itertools.combinations is used to generate all non-repetitive combinations (order irrelevant) that selects a specified number of elements from the iterable object. Its usage includes: 1. Select 2 element combinations from the list, such as ('A','B'), ('A','C'), etc., to avoid repeated order; 2. Take 3 character combinations of strings, such as "abc" and "abd", which are suitable for subsequence generation; 3. Find the combinations where the sum of two numbers is equal to the target value, such as 1 5=6, simplify the double loop logic; the difference between combinations and arrangement lies in whether the order is important, combinations regard AB and BA as the same, while permutations are regarded as different;
Mastering Dependency Injection in Java with Spring and Guice
Aug 01, 2025 am 05:53 AM
DependencyInjection(DI)isadesignpatternwhereobjectsreceivedependenciesexternally,promotingloosecouplingandeasiertestingthroughconstructor,setter,orfieldinjection.2.SpringFrameworkusesannotationslike@Component,@Service,and@AutowiredwithJava-basedconfi
python pytest fixture example
Jul 31, 2025 am 09:35 AM
fixture is a function used to provide preset environment or data for tests. 1. Use the @pytest.fixture decorator to define fixture; 2. Inject fixture in parameter form in the test function; 3. Execute setup before yield, and then teardown; 4. Control scope through scope parameters, such as function, module, etc.; 5. Place the shared fixture in conftest.py to achieve cross-file sharing, thereby improving the maintainability and reusability of tests.
Troubleshooting Common Java `OutOfMemoryError` Scenarios
Jul 31, 2025 am 09:07 AM
java.lang.OutOfMemoryError: Javaheapspace indicates insufficient heap memory, and needs to check the processing of large objects, memory leaks and heap settings, and locate and optimize the code through the heap dump analysis tool; 2. Metaspace errors are common in dynamic class generation or hot deployment due to excessive class metadata, and MaxMetaspaceSize should be restricted and class loading should be optimized; 3. Unabletocreatenewnativethread due to exhausting system thread resources, it is necessary to check the number of threads, use thread pools, and adjust the stack size; 4. GCoverheadlimitexceeded means that GC is frequent but has less recycling, and GC logs should be analyzed and optimized.
How to work with Calendar in Java?
Aug 02, 2025 am 02:38 AM
Use classes in the java.time package to replace the old Date and Calendar classes; 2. Get the current date and time through LocalDate, LocalDateTime and LocalTime; 3. Create a specific date and time using the of() method; 4. Use the plus/minus method to immutably increase and decrease the time; 5. Use ZonedDateTime and ZoneId to process the time zone; 6. Format and parse date strings through DateTimeFormatter; 7. Use Instant to be compatible with the old date types when necessary; date processing in modern Java should give priority to using java.timeAPI, which provides clear, immutable and linear
Understanding the Java Virtual Machine (JVM) Internals
Aug 01, 2025 am 06:31 AM
TheJVMenablesJava’s"writeonce,runanywhere"capabilitybyexecutingbytecodethroughfourmaincomponents:1.TheClassLoaderSubsystemloads,links,andinitializes.classfilesusingbootstrap,extension,andapplicationclassloaders,ensuringsecureandlazyclassloa
