Record the Java interview technical issues I have encountered

1. Java Memory Model

Execution Engineer:java stack/pc registers/native|direct memory Area/java Heap/method Area

Volatile:thread = its own stack + memory cache inside CPU, volatile can make sure read/write directly to main memory data , not local CPU cache

2. Java GC

Serial GC Collector/parallel SCAVENGE/CONCURRENTMS/G1

Java heap:

New Generation/old Generation

New:eden+from/to survivor

Xmn=xmx, Survivorratio, Newratio

Copy/mark-sweep/mark-sweep-compact

Parallel new

Throughput First:

Prallel old

Response Time First:

Cms

3. Inner class and Static Inner class

Inner class contains a reference to their outer class, so it can access its Outers ' class member

Static inner class can only access static filed in it outer class, not require for outer class ' s instance to access Stati C Inner Class

4. Java constructor

123456

父类静态初始化块子类静态初始化块父类初始化块父类构造函数子类初始化块子类构造函数

5. Collection (Wha ' ts the difference between List and Set)

The Java collection is a particularly useful tool class, broadly divided into: Set, list, and map three systems. Where set represents an unordered, non-repeatable set, the list represents an ordered, repeating set, and a map represents a set (key-value pair) that has a mapping relationship. After JDK 1.5, Java adds a queue system collection that represents a collection of queues implementation.

6. How JUnit (Setup/teardown) writes case, how to test exception

@Test (expected = org.springframework.dao.InvalidDataAccessApiUsageException.class)

7. Mock

@Beforepublic void SetUp () {context = new mockery ();/* need to consider security testing in service layer */securitycontex Tholder.getcontext (). Setauthentication (New Usernamepasswordauthenticationtoken ("Admin", "password")); Riskrankdao = Context.mock (Iriskrankdao.class); Context.checking (new Expectations () {{oneof (Riskrankdao). FindAll (); ReturnValue (list)); oneof (Riskrankdao). Save (Riskrank); would (ReturnValue (Riskrank));}); riskranksaved = Riskrankservice.save (Riskrank); context.assertissatisfied (); Assertsame ("riskRankSaved:" + Riskranksaved.tostring () + "Riskrank:" + riskrank.tostring (), Riskrank, riskranksaved);

8. Tdd/scrum

9. Java XML Read-write

DOM, dom4j, JDOM, SAX

Java HASHMAP Implementation & MAP interface

HashMap Internal Data storage:array + link (string/enum is also stored in array), key and its hashcode are used to get Val UE ' s storage index

Internal Stroage Data structure:entry:final key, value, Entry<key, value> Next, Final hashcode

Method:put/get/contains/putall/delete etc

Put:use hashcode to calculate hash value and index it to [0,array.length-1],if Array[i] was empty, point Array[i] to new A dded entry, increase map size; If Array[i] is isn't empty, check whether key exists in link, if yes, modify entry with new value, if not, set Array[i] to n EW added entry and set new added entry ' s next to previous entry, increase HashMap ' s size, if array ' s capacity exceeds it ' Capacity factor (initialized length * factor),resize length = 2 * length. Resize in the multi-threaded unprotected, not only will lead to put/get failure, but also beware of deadlock cycle

Remove:need to modify pervious entry ' s next if elements are not the first one in the link

The difference between Java HashMap and TreeMap

HashMap is faster than TreeMap (Red-black tree), TreeMap contains order

Linux Common commands

File Related:ls, DU/DF, Cat, VI

User Related:chown,chmod,useradd,groupadd

Network Related:tcpdump, Ifcfg,route,netstat

Others:top, Find,rpm,tar,grep, etc

JMS implementation, Queue, topic differences

Producer:destination.send (Message) destination:queue

Consumer Mdb:onmessage Queue

Queue:point to point (1-to-1)

Topic Publish/subscribe (1 to many)

Http://baike.baidu.com/subview/157103/12665866.htm?fr=aladdin

http://blog.csdn.net/cloud_ll/article/details/18228049

14.Spring Benefits

Inverse of control/dependency inject

What libraries are there in Core Java

NETWORK/IO|NIO|AIO/CONCURRENT/COLLECTION/SECURITY/JDBC etc

Synchronized.

Java synchronization, much slower than Java concurrent lock before 1.6, 1.6 slow 20%,1.7 and optimized

Synchronized is used to guarantee the exclusive access of multi-threaded, wait/notify to implement the thread communication, synchronzied lock object, lock is the CPU atomic lock

. SQL Inner/outer Join

Intersection/Set

SQL Statement Tuning

Pagination, some statement design is reasonable, join/like less use

Http://www.cnblogs.com/wxj1020/archive/2008/04/27/1173638.html

How to debug Java OOM

A. What kind of oom:stack? Method Area? Direct Memory Area? Heap area?

B. Heap Area:jmap or Heapdumponoutofmemoryerror | GUI:VISUALVM + Plugins

C. dump file Analysis:eclipse Memory Analyzer, check which class consumes big memories, check which object contains the C Lass

D. From code, check how the class objects is released, what ' s the problem

Record the Java interview technical issues I have encountered