Top 200 pages of Baidu Java interview questions (Part 1)

Baidu "Java interview questions" top 200 pages selected part I

Basic concepts

What is the difference between heap and stack in the operating system? What is the aspect implementation based on annotation? What is the object / relationship mapping integration module? What is the reflection mechanism of Java? What is the connection and difference between acid BS and CS? What are the differences between cookie and session? What are the differences between fail fast and fail safe mechanisms? What are the differences between get and post requests? What are the advantages of interface and abstract class IOC What are the differences between IO and NiO, NiO advantages, what new functions does Java 8 / Java 7 provide us, and what are the race conditions? Give an example. What are the differences between JRE, JDK, JVM and JIT? What technologies do each part of MVC have to implement? How? What is the difference between RPC communication and RMI? Introduction to jswdl development package of Web Service (Web Service). Explanation of jaxp and JAXM. Explanation of soap, UDDI and WSDL. What are the main functions of web container? Please list some common web container names. Can multiple classes be included in a "Java" source file (not an internal class)? What are the limitations? Briefly talk about the class loader you know. Have you implemented class loader? Explain what AOP is (aspect oriented programming) please briefly describe the life cycle of servlet and its related methods. Please briefly describe the principle and implementation steps of Ajax, briefly describe the main functions of struts, what is the n-layer architecture, what is CORBA, what is the purpose, what is java virtual machine, and why Java is called "platform independent programming language" What is a regular expression? What is the purpose? Which package uses regular expressions to achieve pattern matching, what is lazy loading, what is tail recursion, why tail recursion is required, and what are inversion of control and dependency injection

keyword

finalize

1. What is the finalize () method

When is the finalize () method called? What is the purpose of the destructor? What is the difference between final and finalize

2. What are the usages of the final keyword

Where can the final and static keywords be used? What are the differences between final, finally and finalize? What are the differences between final, finalize and finally?

3. Can I assign value to static final type at runtime

When you use the final keyword to modify a variable, whether the reference cannot be changed or the referenced object cannot be changed. What does it mean when a class is declared as final? What does throw, throw, try, catch and finally mean

How many modifiers does java have? What are they used to modify

volatile

What is the practice of volatile modifiers? What are volatile variables? What is the difference between volatile variables and atomic variables? What guarantee does volatile type variables provide? Can you make a non atomic operation atomic? Can you create a volatile array?

What are the characteristics of transient variables? When super uses public static void to write static public void? How to explain the role of each keyword in the statement of public static void main (string args []). Please state the scope public, private, protected, and the difference when it is not written. Is sizeof a Java keyword

static

What is the difference between static class and non static class? What does the static keyword mean? Can you override a private or static method in Java? What are the characteristics of static types? Why must the main () method be static? Can you declare the main () method as non static? Can you call non static methods from within a static method? When are static variables loaded? During compilation or run? When are static code blocks loaded? Can member methods access static variables? Why can't static methods access member variables

switch

What type of data can the expression in the switch statement be? Can the switch act on byte, long, string? What is the difference between the while loop and the do loop

Operator

&What is the difference between operator and & & operator? What is the difference between a = a + B and a + = B? The difference between logical operators (&, |, ^) and conditional operators (& &, |). 3 * 0.1 = = 0.3 what will be returned? True or false? float f=3.4; Is it correct? short s1 = 1; s1 = s1 + 1; What's wrong?

data structure

Foundation types (primitives)

What is the difference between primitives and wrappers? Briefly describe the sizes of the nine basic data types and which of their encapsulation classes int and integer will occupy more memory? What's the difference between int and integer? When does the parseint() function use the default values of float and double? How to round the decimal point and keep the two digits after the decimal point? Can a Chinese character be stored in a char type variable? Why

Type conversion

How to convert bytes to long type how to convert bytes to string how to convert numeric characters to numbers can we cast int to a variable of byte type? If the value is larger than the range of byte type, what will happen? Can a double value be assigned to a variable of long type without coercion? What is type down conversion

array

How to balance whether to use an unordered array or an ordered array, how to judge whether the array is null or empty, and how to print the array? How to print duplicate elements in an array? What is the difference between array and ArrayList? When should array be used instead of ArrayList array and linked list data structure description? Is there a length () method for each time complexity array? Does string have a length () method

queue

What are queues and stacks? List their differences. What is BlockingQueue? Briefly describe the use and differences of concurrentlinkedqueue and linkedblockingqueue.

Storage performance and characteristics of ArrayList, vector and LinkedList string

StringBuffer

What is the difference between ByteBuffer and StringBuffer

HashMap

What is the working principle of HashMap? What is the internal data structure? How to determine the capacity of HashMap's table? What is LoadFactor? How does this capacity change? What problems will this change bring? What is the data structure implemented by HashMap? How to realize the difference between HashMap, hashtable and concurrenthashmap? The traversal mode and efficiency of HashMap. The difference between HashMap, linkedmap and treemap. How to decide whether to choose HashMap or treemap? What if the size of HashMap exceeds the capacity defined by load factor? Is HashMap thread safe? What are the maps used in concurrency and their internal principles, such as storage mode, hashcode, capacity expansion, default capacity, etc

HashSet

What is the difference between HashSet and TreeSet? How does HashSet work internally and how does weakhashmap work?

Set

Elements in a set cannot be repeated, so what method is used to distinguish whether they are repeated or not? Is it = = or equals()? What's the difference between them? Treemap: what tree is used to implement treemap? The difference between treemap, HashMap and lindedhashmap. How do treemap and TreeSet compare elements when sorting? How do the sort () method in the collections tool class compare elements? TreeSet: how to complete reverse sorting for a built TreeSet. What is enumset

Hash algorithm

Brief description of the function of hashcode consistency is it possible that two unequal objects have the same hashcode? What happens when two objects have the same hashcode? How to get the value object? Why do you need to override the hashcode method when overriding the equals method? What are the similarities and differences between equals and hashcode? What is the use of A. hashcode()? What is the relationship with A. equals (b)? Where is the importance of hashcode () and equals () methods? Object: what are the common methods of object? Object class hashcode, equals design principle? Why does Sun design like this? Overview of object class how to automatically complete all hashcode and equals implementations for child classes in the parent class? What are the advantages and disadvantages of doing so. Can I use random numbers in hashcode()?

LinkedHashMap

What is the difference between LinkedHashMap and PriorityQueue

List

What are the characteristics of list, set and map interfaces when accessing elements? List, whether map inherits from the collection interface, and what are the different ways to traverse a list

LinkedList

Is LinkedList a one-way linked list or a two-way linked list? What are the differences between LinkedList and ArrayList? Describe the concepts of collections, interfaces and implementations in Java. What are the differences between LinkedList and ArrayList? Who is faster in ArrayList, LinkedList and vector when inserting data?

ArrayList

The default size of ArrayList and HashMap is the difference between most ArrayList and LinkedList. When to use ArrayList? What is the difference between ArrayList and set? The difference between ArrayList and vector. How is ArrayList implemented? The difference between ArrayList and LinkedList. How is ArrayList expanded? What is the difference between array and ArrayList? When is it more appropriate to use array to describe the storage performance and features of arralist, vector and LinkedList

Map

What are the different collection views provided by map, list, queue and stack? Why does the map interface not inherit the collection interface

Collections

Introduces the collection framework in Java. What are the basic interfaces of the collection class framework? What are the collections classes? What is the difference between collections and collections? What are the best practices for implementing the collection class framework of collection and map? Why does collection not inherit from clonable and serializable interfaces? What are the best practices for using collections in Java? Differences between legacy classes (hashtable, vector) and existing classes in Collections

What is a B + tree, B-tree, and list the actual use scenarios.

Interface

What does the comparator and comparable interface do? List their differences

object

Copy (clone)

How to implement object cloning? How to distinguish between deep copy and shallow copy? How to implement the activation mechanism? When writing the clone () method, there is usually a line of code. What is it

compare

When comparing objects, what is the difference between the "= =" operator and the equals operation? If you want to override the equals method of an object, you should also consider what two objects have the same value (x.equals (y) = = true), but can have different hash codes, right

constructor

What is a constructor chain? The order in which constructors are called when objects are created

Immutable object

What is immutable object? Why is string immutable in Java? How to build immutable class structure? The key point is where to create an immutable object containing variable objects

How to sort a group of objects

method

Can a constructor be overridden (override) can methods be both static and synchronized? Can abstract's method be both static and native? What kind of parameter passing type does Java support? An object is passed to a method as a parameter, value or reference. When an object is passed to a method as a parameter After, this method can change the properties of this object and return the changed results. So, is this value transfer or reference transfer? Can we overload the main () method? What happens if the main method is declared private

GC

concept

What is GC? Why is there a GC? When will it lead to garbage collection? How does the GC run? What are the old and new and what are the permanent areas? There are several ways of GC? How to configure when an object will be GC? How to determine whether an object survives system gc() Runtime. What does GC () do? Can GC execution be guaranteed? Can the garbage collector reclaim memory immediately? Is there any way to actively notify the virtual machine for garbage collection? When does minor GC, major GC, young GC and full GC happen? Implementation principle of garbage collection algorithm. If the reference of the object is set to null, will the garbage collector release the memory occupied by the object immediately? What are the best practices for garbage collection

What are the GC collectors

What is the basic principle of garbage collector? What is the difference between serial collector and throughput collector? What are the differences between serial and parallel GC? The characteristics and differences between CMS collector and G1 collector? What is the working process of CMS garbage collector and a complete GC process in JVM? How can objects be promoted to the old age of throughput first and response first garbage collector selection

GC policy

For a practical scenario, if a GC policy is selected, will garbage collection occur in the permanent generation of the JVM

Collection method

Principle and characteristics of mark clearing, mark sorting and copying algorithm? Where are they used? What ideas do you have if you can optimize the collection method

JVM

parameter

Tell me about the main JVM parameters you know - XX: + usecompressedoops

Classloader

What JVMs do java class loaders have and how do they load bytecode files

memory management

What are the memory areas of the JVM? What is the role of each area? How does an object survive and transfer in these parts from creation to destruction? Explain the usage of stack, heap and method area in memory. Which parameter in the JVM is used to control the stack of processes? Brief description of memory allocation and recycling strategy, brief description of reordering, memory barrier, happy before, Is there a memory leak in main memory and working memory Java? Please give an example to briefly describe soft reference, weak reference and virtual reference in Java

What is the memory mapped cache

The above is the whole content of this article. I hope it will be helpful to your study, and I hope you can support programming tips.