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What is the implementation mechanism of java polymorphism?

The implementation mechanism of Java polymorphism is: the reference variable defined by the parent class interface or interface can point to the instance object of the subclass or implementation class, and the method called by the program is dynamically bound at runtime, which is the specific implementation object pointed by the reference variable. Methods.

May 16, 2020 am 11:04 AM

java 多态

What are the main data structures in java

The data structures in Java are: 1. Stack, which implements a last-in-first-out data structure; 2. Dictionary, which is an abstract class that defines a data structure that maps keys to values; 3. Enumeration, which The retrieval interface defines a way to retrieve consecutive elements from a data structure.

May 16, 2020 am 10:38 AM

java 数据结构

What is the difference between T and ? in java generics?

The difference between T and ? in Java generics is: T represents an unknown type, which is used as a parameter in a method or a class generic; ? represents a general reference in generics, which is a placeholder character, data cannot be added to the container.

May 16, 2020 am 09:58 AM

java 泛型 T ?

How to define string in java

The method of defining a string in Java is: 1. Define it through direct assignment, the specific code is [String str = "Hello";]; 2. Define it through instantiation through the construction method, the specific code is [String str = new String( "Hello");].

May 15, 2020 am 11:35 AM

java 字符串

What is the difference between queue and stack in java

The difference between a queue and a stack in Java is: 1. The queue is first in, first out, and the stack is first in, last out; 2. The queue is implemented by the Queue interface, and the stack is implemented by the List interface; 3. The stack can only be inserted and deleted at one end of the table Operation, the queue performs insert operations on one end of the table and delete operations on the other end.

May 15, 2020 am 11:21 AM

java 队列栈

Can interface implement interface in java?

Interfaces cannot implement interfaces in java. An interface can inherit one or more interfaces. To inherit an interface, you need to use the extends keyword. A sub-interface inherits the methods of the parent interface, such as [public interface Hockey extends Sports, Event].

May 15, 2020 am 11:04 AM

java 接口

What are the several states of java threads?

The several states of java threads are: 1. NEW; 2. RUNNABLE; 3. BLOCKED; 4. WAITING; 5. TIMED_WAITING; 6. TERMINATED.

May 14, 2020 pm 03:53 PM

java 线程

How to declare an array in java

The method of declaring an array in Java is: taking a one-dimensional array as an example, the method of declaring an array is [array type [] array name], such as [int[] array = {1,2,3}] or [int[] array = new int[] {1,2,3}], which means declaring an array named int type.

May 14, 2020 pm 03:14 PM

java 数组

What is a static variable in java

Static variables in Java refer to variables modified by the static keyword, also called class variables. Static variables can be accessed directly through the class name, their life cycle depends on the life cycle of the class, and they can be shared by all instances of the class.

May 14, 2020 pm 02:01 PM

java 静态变量

What is the difference between java variables and constants

The difference between Java variables and constants is: 1. In the Java coding standards, constant names are required to be in uppercase, and variable names are required to be in lowercase; 2. Constants can only be assigned once, and variables can be assigned multiple times; 3. Constants are used during the running of the program. It cannot be changed, variables can be changed.

May 14, 2020 pm 01:33 PM

java 变量常量

What is the difference between java interface and abstract class

The difference between Java interfaces and abstract classes is: 1. Abstract classes can not only have abstract methods, but also instance methods. All methods in the interface are public abstract methods; 2. Subclasses use the extends keyword to inherit abstract classes, and subclasses Use the implements keyword to implement the interface.

May 14, 2020 pm 01:15 PM

java 接口抽象类

What are the four commonly used frameworks for java development?

The four commonly used frameworks for Java development are: 1. SpringMVC, which implements the MVC design pattern; 2. Mybatis, which is an excellent persistence layer framework; 3. Spring, which provides IOC, AOP and other functions; 4. Maven , which is a project management tool.

May 13, 2020 pm 04:20 PM

java 框架

What are the keywords of java exception handling

The keywords of java exception handling are: 1. try; 2. catch; 3. finally; 4. throw; 5. throws. All exception classes are subclasses inherited from the java.lang.Exception class.

May 13, 2020 pm 01:31 PM

java 异常处理关键字

What technologies do you need to master for java back-end development?

The technologies that need to be mastered in java back-end development include: 1. Servlet, Servlet plays the core role in the Web MVC structure; 2. JDBC, RMI, etc.; 3. Spring framework; 4. Combined with hadoop to build java distributed development.

May 12, 2020 pm 02:11 PM

java 技术