core java questions

= table; int newcapacity = Newtable.length; for (int j = 0; J Brief summary对于HashSet及其子类而言，它们采用hash算法来决定集合中元素的存储位置，并通过hash算法来控制集合的大小；对于HashMap、Hahstable及其子类而言，它们采用hash算法来决定Map中key的存储，并通过hash算法来增加key集合的大小。hash表里可以存储元素的位置被称为桶（bucket），通常情况下，每个桶里存储一个元素，此时有最好的性能，hash算法可以根据hashCode值计算出桶的存储位置，接着从桶中取出元素。但hash表的状态是open的：在发生hash冲突的情况下，单个桶会存储多个元素，这些元素以链表形式存储，必须按顺序搜索。HashSet和HashMap的hash表都包含如下属性：- 容量capacity:hash表中通的数量- 初始化容量initial capacity：创建hash表时桶的数量。- 尺寸size：当前hash表中记录的数量- 负载因子load f

, in the programming language, threading can be a love-hate paradox for programmers, which can greatly simplify the model, help programmers write powerful code, and, on the other hand, make our programs appear with a variety of bugs that can be difficult to reproduce in the development environment. Here the author based on the "Java Core technology" book and some Bovinlai to share with you on

To prepare to learn the next Java, according to the "core Java" content, simply made a note. There are many places in this book that compare the syntax of C + + and Java, so it's very advantageous for those who turn from C + + to Java!Javac Xxx.javajava XXXJava Applet:applet

complete most functions of the field****************An iterator is a design pattern that is an object that can traverse and select objects in a sequence, and the developer does not need to know the underlying structure of the sequence . Iterators are often referred to as "lightweight" objects because they are less expensive to create.The iterator functionality in Java is relatively simple and can only be moved one way:(1) Use Method iterator () "Call

Java operating mechanism the JVM of the core mechanism The JVM is the runtime environment for Java programs The JVM is part of the JRE, it is a fictitious computer, or it can be understood that the bytecode file is interpreted as a machine instruction on a specific platform when the byte code file is executed by the CPU JVM with the byte code as the machine in

Note: This article is reproduced from http://www.cnblogs.com/huajiezh/p/5790928.html, the copyright belongs to its all! Summary of common questions in JavaFirst, the Java Foundation1. Why is the string class final?2, HashMap The source code, the realization principle, the bottom structure.3, say that you know a few Java Collection class: List, set, queue, map imp

Recently I read core Java, but I have never understood it before. I have read many posts and blogs and finally understood it. In Java, the char [], String, stringbuilder and stringbuffer class adopts UTF-16 encoding, using U + 0000 ~ U + FFFF represents a basic character (BMP character), but Char located in U + d800 to U + dbff and U + dc00 to U + dfff is conside

in any order, but are always retrieved in sorted order. Whenever the Remove method is called, the smallest element in the current priority queue is always fetched, but the priority queue is not sorted.Use data Structure = = "HeapThe heap is a self-adjusting two-fork tree. You can have the smallest elements move to the tree root without having to spend time sorting.Typical case: Task schedulingPriorityqueue ();Constructs a priority queue for holding compareable objectsPriorityqueue (int initialc

InstantiationException, IllegalAccessException { returnnew PairnewInstance(), c.newInstance());}CallmakePair(Employee.class);The type parameter T matches the Employee.Generic type information in a virtual machineYou can use the reflection API to determine: This generic method has a type parameter called T. This type parameter has a subclass qualification, which is itself a generic type. This qualified type has a wildcard parameter. This wildcard parameter has a superclas

[Java Study Notes] Chapter 5 inheritance of Java core technologiesChapter 2 Inheritance Using inheritance, You can construct a new class based on an existing class. Inheriting existing classes is to reuse (inherit) the methods and domains of these classes. You can also add new methods and domains. Reflection.5.1 superclass subclass Use extends to construct a deri

Java -- JDK dynamic proxy core source code parsing, java -- jdk source code 1. First, let's take a look at how to use JDK dynamic Proxy: Public static void main (String [] args) {/*** creates a Bean object that implements the BeanInterFace interface */BeanInterFace bean = new Bean (); /*** create a MyProxy object that implements the InvocationHandler interface an

simple test, that is, do not use the exception to do the program to determine the branch; 2) to properly use the exception hierarchy, throw or capture, to try to use a class that can express a specific purpose, which will have better readability, Do not use throwable at all times, so that the readability is poor, 3) in the detection of errors, "harsh" than laissez-faire better, such as Stack.pop () is the return of NULL better or run out emptystackexception better? The author thinks the latter

IncreaseDeleteThe Remove method allows you to delete a specified element.Find*************************************************HashSet can neither use the index of 0 1 2 3 to determine the value of an element, nor use key to determine the value of an element*********************HashSet like this ["AA", "BB"] grow into such a data structure******************HashMap grow into such {a=123, B=hello}Jsonobject very much like {"A": 123, "B": null} *hashmap* *hashset*

"Original" https://www.toutiao.com/i6594587397101453827/Java Core Data structure (List,map,set) usage tips and optimizationsJDK provides a set of major data structure implementations, such as list, MAP, set and other common data structures. This data is inherited from the Java.util.Collection interface and is located in the Java.util package. 1. List interface The three most important list interface impleme

called and passed to it with the methods object and the original invocation parameters. The calling processor must give a way to call processing.To create a proxy object, you need to use the Newproxyinstance method of the proxy class, which has three parameters:1: Class loader. As part of the Java security model, for system classes and from other classes, you can use a different classloader, currently using the default class loader with null notation

Observer observer the message and the event is one, the difference is that when inheriting Java codeChanges in different ways.The triggers in the database are somewhat like this, but they are not generally compared.Similar to the Django views.py, how does the Web. XML modify the code so that it can map URLs to the actual file address?Set Jsp-file-servlet-name, Url-pattern- servlet-name, to get Url-pattern to jsp-file mappings.I want to change the Web

not recommend not knowing when to callPackage import with ingest package is similar to reference namespacePackage = = NamespaceImport = = usingStatic ImportClass Design Tips1) Guaranteed Data privacy2) Initialize the data3) Do not use the base type too much in the class (you can use the aggregation relationship instead)4) Not all domains require separate accessors and converters5) Decomposition of classes with excessive responsibilities6) The class name and method name should be able to reflect

. Cannot instantiate a type variable, cannot construct a generic arrayCannot be new T (...), new t[] or t.class, because when the type is erased, T becomes the object typeor Object[2],new object () is not what we want to see, you can use reflection to create an objectFirst. T.class is not legal.public static {try{return new Pair}catch (Exception ex){return null}}Pair6. Invalid type variable in static context of generic classCannot reference a type variable in a static field or methodpublic class

callable object, save the returned future object. When no more tasks are committed, call shutdown. Scheduled executionThe Scheduledexecutorservice interface has a method that is designed for scheduled execution or repetitive execution of tasks. The latter two methods implement this interface.Control task groupsThe InvokeAll method submits all objects to a collection of callable objects and returns a list of future objects that represent the solution for all tasks.Fork-join FrameSome ap

Alas, the front has been skipped, a look at the pure text description on the headache.This section is about Java data types, there are eight basic types, of which the int,short,long,byte four are shaped, is pure numbers, the size is 4,2,8,1 bytes, a byte is composed of 8 01, the highest bit is the sign bit, 0 is an integer, 1 is a negative number, For example, the range of byte is 128 to 127. I don't know the rest of it.Floating-point types have float