java certification test questions

One, the choice question 1, access modifier scope from large to small is () A. Private-default-protected-public B.public-default-protected-private C,private-protected-default-public D,public-protected-default-private 2, the following () is not a method of object class. A.clone () b.finalize () c.tostring () D.hasnext () 3. In Java, the following () interfaces are used to store objects in a key-value manner. A. java.util.Collection B.java.util.map C.ja

, regardless of whether the assertion is enabled. However, you can test the post condition with assertions in a public method or in a Non-public method. In addition, assertions should not change the state of the program in any way. What is the GC, VIII? Why should there be a GC? (Basis). GC is a garbage collector. Java programmers do not have to worry about memory management because the garbage collector

objects of this class are used in a multithreaded environment, it is best to use StringBuffer. 39. How do I convert a comma-delimited string into an array? Reference: (1) with regular expressions, the code is roughly: ' string[] result = Orgstr.split (","); ' (2) with StringTokenizer, code:StringTokenizer Tokener = StringTokenizer (Orgstr, ",");String[] result = new String[tokener.counttokens ()];int i = 0;while (Tokener.hasnext ()) {result[i++] = Tokener.nexttoken ();}40. 数组有没有length()方法？Strin

simply use an index instead of creating an iterator object. Linklist also creates objects for each inserted element, all of which you have to understand that it also brings additional overhead.Finally, in the book Practical Java, Peter Haggar suggests using a simple array instead of a vector or ArrayList. This is especially true for programs with high efficiency requirements. Because the use of arrays (array) avoids synchronization, additional method

　　As the first Dark Horse technical blog It is necessary to explain the background. The personal understanding of the blog is to be used in communication, in his study, in the exchange of learning to grow together. Let's get down to the chase. This article is mainly to introduce the black horse in the introduction of testing some of the problems (this should not leak the question bank).First analysis of 10 sets of questions, mostly is the basic knowle

. LOG4J uses the log-level mechanism to write out the log output level in order of output levels from low to high.Answer: log4j is divided into off, FATAL, ERROR, WARN, INFO, DEBUG, all or the level you define. LOG4J recommends using only four levels, with the priority from high to low being ERROR, WARN, INFO, DEBUG. By defining the level here, you can control the switch to the appropriate level of log information in your application. For example, if the info level is defined here, the log infor

instability or even crashes, The GC mechanism provided by Java can automatically monitor whether an object exceeds the scope to achieve the purpose of automatically reclaiming memory, and the Java language does not provide an explicit way to dispose of the allocated memory.20. Write a singleton mode (Singleton)//第一种 ：饿汉模式public class SingleTon{ private SingleTon(){} //实例化放在静态代码块里可提高程序的执行效率，但也可能占用更大的空

similarities and differences between JSP and servlet?JSP is the extension of servlet technology, is essentially a simple way of servlet, JSP more emphasis on the application of the appearance of expression, compiled is "class servlet." The main difference between Servlets and JSPs is that the application logic of the servlet is in the Java file and is completely detached from the HTML in the presentation layer, whereas the JSP case is that

://blog.csdn.net/garfielder007/article/details/54432322Structure of the 2,java heap and the permanent generation of pairs (renamed to meta-space after Java8)Heap memory is used to hold objects and arrays created by newPermanent generation (to be sorted): http://www.cnblogs.com/paddix/p/5309550.htmlHttps://www.nowcoder.com/questionTerminal/5c3dc3914da548e5b0617f4da9da7488?pos=208orderByHotValue=13, Regular expressionThis is still to see the Novice tuto

**Record some Java written exams, and interview with less certain questions:The difference between 1,string,stringbuffer,stringbuilder2,servlet is a single instance or multi-instance3,hashmap4,hibernate, the three object states of the session5,javascript closure, JS get form There are also sessions in 6,web, where the SessionID is allocated, the session expires when the browser is closed, and SessionID also exists in the client's cookie,When it shuts

indicates whether the FETCH statement returns rows from the active set, such as a row is not returned, the value of this property isTrue? (select 1 items)A.%foundB.%notfoundC.%rowcountD.%isopenAnswer: B%found Boolean property, True if the record was last read successfully;%notfound boolean attribute, opposite to%found;%isopen Boolean property that returns TRUE when the cursor is open;%rowcount Numeric property, returns the number of records that have been read from the cursor212. Which clause i

) { account + + money; }NBSP ; } } class Newthread Impleme NTS Runnable { private Bank bank; Public Newthread (Bank) { This.bank = bank; } @Override public void Run () {nbsp for (int i = 0; i Common methods for ThreadLocal ThreadLocal (): Creating a thread local variable get (): returns this The value in the current thread copy of the thread local variable initialvalue (): Returns the current thread's "initial value" set (T

-operatorThe non-operator is denoted by the symbol "~", and its Operation law is as follows:If the bit is 0, the result is 1, if the bit is 1, the result is 0, see a simple example below.public class Data15{public static void Main (string[] args){int a=2;SYSTEM.OUT.PRINTLN ("A non-result is:" + (~a));}}4. Xor operatorThe XOR operator is denoted by the symbol "^", and its Operation law is:The two operand bits, the same result is 0, and the result is 1. Let's look at a simple example.public class

to synchronize No isK,v can null whetherHashMap is a lightweight implementation of Hashtable (non-thread-safe implementation), they all complete the map interface,The main difference is that HASHMAP allows null (NULL) key values (key), which may be more efficient than Hashtable due to non-thread safety.HashMap allows NULL to be used as a entry key or value, and Hashtable is not allowed.HashMap hashtable contains method removed, changed to Containsvalue and ContainsKey. Because the contains meth

Directory 1 Problem Description 2 Solutions 1 problem description Problem DescriptionXiaoming has been thinking of such a strange and interesting question these days:How many 1~n are there in one of the full permutations of the series? The definition of the number of intervals mentioned here is:If all the elements in the interval [L, R] (that is, the first l to the r elements of this arrangement) are incremented, a "continuous" sequence of lengths of R-l+1 is obtained, which is call

(Various companies interview original questions) online has done a set of CC ++ integrated test questions, also to test your level (2), cc integrated test questions I have read the last 10 que