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This article introduces the relevant knowledge of "what are the basic interview questions of big data". In the operation of actual cases, many people will encounter such a dilemma. Next, let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

1. Can multiple classes (not inner classes) be included in a ".java" source file? What are the restrictions? [basic]

Answer: yes; only one class name must be the same as the file name.

1. Name some commonly used classes, packages and interfaces, please name 5 each. [basic]

Answer: commonly used class: BufferedReader BufferedWriter FileReader FileWirter String Integer

Commonly used package: java.lang java.awt java.io java.util java.sql

Common interface: Remote List Map Document NodeList

2. Can Anonymous Inner Class (anonymous inner class) extends (inherit) other classes? Is it possible to implements (implement) interface (interface)? [basic]

Answer: you can inherit other classes or implement other interfaces, which is often used in swing programming.

3. Can the inner class refer to the members of the class it contains? Are there any restrictions? [basic]

Answer: an inner class object can access the contents of the external class object that created it.

4. What is the mechanism for implementing polymorphism in java? [basic]

A: overlay Overriding and overloaded Overloading of the method are different manifestations of java polymorphism.

Covering Overriding is a manifestation of polymorphism between parent and subclass.

Overloading Overloading is a manifestation of polymorphism in a class.

5. What does it mean when a class is declared as a final type in java? [basic]

A: indicates that this class cannot be inherited and is a top-level class.

6. Which of the following classes can be inherited? [basic]

1) java.lang.Thread (T)

2) java.lang.Number (T)

3) java.lang.Double (F)

4) java.lang.Math (F)

5) java.lang.Void (F)

6) java.lang.Class (F)

7) java.lang.ClassLoader (T)

Answer: 1, 2, 7 can be inherited.

7. Point out the running result of the following program: [basic]

Class A {

Static {

System.out.print ("1")

}

Public A () {

System.out.print ("2")

}

}

Class B extends A {

Static {

System.out.print ("a")

}

Public B () {

System.out.print ("b")

}

}

Public class Hello {

Public static void main (String [] ars) {

An ab = new B (); / / executed here, the result: 1a2b

Ab = new B (); / / execute here, the result: 1a2b2b

}

}

Answer: the output is 1a2b2b; the static code snippet of the class can be thought of as the code executed by the class loading (virtual machine loading) for the first time, while for class loading, you first execute the construction of its base class, and then perform its own construction.

8. The execution order of classes when inheriting is usually a multiple choice question. What will you print out? [basic]

Parent class:

Package test

Public class FatherClass {

Public FatherClass () {

System.out.println ("FatherClass Create")

}

}

Subcategory:

Package test

Import test.FatherClass

Public class ChildClass extends FatherClass {

Public ChildClass () {

System.out.println ("ChildClass Create")

}

Public static void main (String [] args) {

FatherClass fc = new FatherClass ()

ChildClass cc = new ChildClass ()

}

}

A: the output result is:

FatherClass Create

FatherClass Create

ChildClass Create

9. How to implement the inner class? [Foundation]

A: the sample code is as follows:

Package test

Public class OuterClass {

Private class InterClass {

Public InterClass () {

System.out.println ("InterClass Create")

}

}

Public OuterClass () {

InterClass ic = new InterClass ()

System.out.println ("OuterClass Create")

}

Public static void main (String [] args) {

OuterClass oc = new OuterClass ()

}

}

The output is as follows:

InterClass Create

OuterClass Create

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