传值 / 传引用

  1. 对象就是传引用
  2. 原始类型就是传值
  3. String等immutable类型因为没有提供自身修改的函数,每次操作都是新生成一个对象,所以要特殊对待。可以认为是传值。


  • Overlading vs. Overriding
    • Overloading is a term used to describe when two methods have the same name but differ in the type or number of arguments
    • Overriding occurs when a method shares the same name and function signature as another method in its super class
  • ArrayList
    • ArrayList myArr = new ArrayList();
    • myArr.add(one);
    • System.out.println(myArr.get(0));
  • Vector
    • Vector myVect = new Vector();
    • myVect.add(one);
    • System.out.println(myVect.get(0));
  • LinkedList
    • LinkedList myLinkedList = new LinkedList();
    • myLinkedList.addFirst(two);
    • myLinkedList.addFirst(one);
    • Iterator iter = myLinkedList.iterator();
    • while (iter.hashNext()) { System.out.println(; }
  • HashMap
    • HashMap map = new HashMap();
    • map.put(one, uno);
    • map.put(two, dos);
    • System.out.println(map.get(one));


Private Constructor: In terms of inheritance, what is the effect of keeping

This has direct implications for inheritance, since a subclass calls its parent's constructor. The class A an be inherited, but only by its own or its parent's inner classes.

Return from Finally: In java, does the finally block get executed if we insert a return statements inside the try block of a try-catch-finally?

Yes, it will get executed. The finally block gets executed when the try block exits.

There are some cases in which the finally block will not get executed, such as the following:

  • If the virtual machine exits during try/catch block execution
  • If the thread which is executing during the try/catch block gets killed

Final, etc.: What is the difference between final, finally, and finalize?

  • final - control whether a variable, method, or class is change-able
  • finally - used in a try/catch block to ensure that a segment of code is always executed
  • finalize() - called by garbage collector once it determines that no more references exist.

Generics vs. Templates: Explain the difference between templates in C++ and generics in Java?

The implementation of Java generics is rooted in an idea of type erasure. This technique eliminates the parameterized types when source code is translated to the Java Virtual Machine (JVM) byte code.

The use of Java generics didn't really change much about our capabilities; it just made things a bit prettier. For this reason, Java generics are sometimes called syntactic sugar

In C++, templates are essentially a glorified macro set, with the compiler creating a new copy of the template code for each type.

TreeMap, HashMap, LinkedHashMap: Explain the differences between these three. Provide an example of when each one would be best

  • HashMap offers O(1) lookup and insertion. It is implemented by an array of linked lists.
  • TreeMap offers O(log N) lookup and insertion. Keys are ordered. It is implemented by a Red-Black Tree.
  • LinkedHashMap offers O(1) lookup and insertion. Keys are ordered by their insertion order. It is implemented by doubly-linked buckets.

Object Reflection: Explain what object reflection is in Java and why it is useful.

Provides a way to get relfective information about Java classes and objects, and perform operations such as:

  • Getting information about the methods and fields present inside the class at runtime.
  • Creating a new instance of a class
  • Getting and setting the object fields directly by getting field reference, regardless of what the access modifier is.

Three main reasons why Object Reflection is Useful:

  1. It can help you observe or manipulate the runtime behavior of applications
  2. It can help you debug or test programs, as you have direct access to methods, constructors, and fields.
  3. You can call methods by name when you don't know the method in advance.


  • 垃圾回收机制。。。(主要从下面几方面解答 GC原理、最好画图解释一下年轻代(Eden区和Survival区)、年老代、比例分配及为啥要这样分代回收)
  • 对象分配问题,堆栈里的问题,详细的会问道方法区、堆、程序计数器、本地方法栈、虚拟机栈,问题入口从String a,new String("")开始
  • 关键字,private protected public static final 组合着问
  • Object类里面有哪几种方法,作用
  • equals 和 hashCode方法,重写equals的原则()
  • 向上转型
  • Java引用类型(强引用,软引用,弱引用,虚引用)
  • 线程相关的,主要是volitate,synchorized,wait(),notify(),notifyAll(),join()
  • Exception和Error
  • 反射的用途
  • HashMap实现原理(数组+链表),查找数据的时间复杂度
  • List有哪些子类,各有什么区别
  • NIO相关,缓冲区、通道、selector。。。(不熟,面了这么多,挂在这里。其实主要是表现在同步阻塞和异步,传输方式不同。标准IO无法实现非阻塞模式、文件锁、读选择、分散聚集等)
  • 内存泄露,举个例子
  • OOM是怎么出现的,有哪几块JVM区域会产生OOM,如何解决(对于该问题,建议去《Java特种兵》的3.6章)
  • Java里面的观察者模式实现
  • 单例实现(我一般用enum写,不容易被挑毛病)
  • 用Java模拟一个栈,并能够做到扩容,并且能有同步锁。(用数组实现)
  • Java泛型机制,泛型机制的优点,以及类型变量