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What is a collection in java

A collection in Java is a container for data, to be precise, a container for data object references. 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.

Nov 11, 2019 pm 01:22 PM

java

How to enter in java

Input method in java: First import the java.util.Scanner package at the beginning of the program; then use new Scanner to create a Scanner object; finally use the nextLine, nextInt, and nextDouble methods to obtain the input data.

Nov 11, 2019 pm 01:19 PM

java输入

what is java multithreading

A Java thread is an execution path or a control unit within a process; Java multi-threading refers to the existence of multiple threads in a process, and multi-threading can improve program execution efficiency.

Nov 11, 2019 am 11:57 AM

java多线程

How to understand the concept of rewriting in java

Overriding in Java refers to the situation where there are two methods with the same name and parameter list in the Java subclass and the parent class. Among them, the parameter list of the overridden method must be exactly the same as the parameter list of the overridden method.

Nov 11, 2019 am 11:51 AM

java重写理解概念

What is java abstract class

A Java abstract class is a class modified with the abstract keyword. This class is called an abstract class. An abstract class is a collection of public attributes of all its subclasses and a class that contains one or more abstract methods.

Nov 11, 2019 am 11:48 AM

java

what are java generics

Java generics means that the type is parameterized from the original specific type, similar to the variable parameters in the method. At this time, the type is also defined in parameter form, and then the specific type is passed in when using/calling.

Nov 11, 2019 am 11:40 AM

java泛型

Can java interfaces be inherited?

Java interfaces can be inherited, and it is multiple inheritance, but only interfaces can inherit interfaces, and classes can only implement interfaces. An interface can inherit another interface or multiple interfaces, and a common class can implement multiple interfaces.

Nov 11, 2019 am 11:23 AM

java

how to run java

How to run java: First download and install [JDK 6.0]; then create a new variable in the computer system variables, the variable name is [JAVA_HOME] and enter [cmd] in the run window; then create a new variable in the root directory of the C drive subdirectories and java files; finally run java in the command line window.

Nov 11, 2019 am 11:22 AM

java

The difference between java interface and abstract class

The difference between a Java interface and an abstract class: All methods in an interface are implicitly abstract; while an abstract class can contain both abstract and non-abstract methods. A class can implement many interfaces, but can only inherit one abstract class. An abstract class can implement an interface without providing implementations of the interface methods.

Nov 11, 2019 am 11:18 AM

java

what are java environment variables

Java environment variable refers to a parameter in the operating system's running environment. After configuring the java environment variables, you can use java and javac commands anywhere in the system. When executing commands, you no longer need to enter the bin directory under the java installation directory.

Nov 11, 2019 am 11:12 AM

java环境变量

The difference between java classes and interfaces

The difference between Java classes and interfaces: All properties of interfaces are public static final; all classes are public by default; subclasses can only inherit one parent class (extends) and can inherit multiple interfaces (implement).

Nov 11, 2019 am 11:08 AM

java

what is java inheritance

Java inheritance is a technology that uses the definition of an existing class as a basis to create a new class. The definition of a new class can add new data or new functions, or use the functions of the parent class, but it cannot selectively inherit the parent class. This technology makes it very easy to reuse previous code, which can greatly shorten the development cycle and reduce development costs.

Nov 11, 2019 am 10:48 AM

java继承

How to connect to database in java

Java uses JDBC to connect to the database. It is a Java API used to execute SQL statements and can provide unified access to a variety of relational databases. It consists of a set of classes and interfaces written in the Java language.

Nov 11, 2019 am 10:45 AM

java

What is reflection mechanism in java

The Java reflection mechanism is in the running state. For any class, all properties and methods of this class can be obtained, and for any object, any of its properties and methods can be called.

Nov 11, 2019 am 10:37 AM

java