Recent questions tagged Java

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java - Sorting large data using MapReduce/Hadoop

I am reading about MapReduce and the following thing is confusing me. Suppose we have a file with 1 ... missing something? Thanks, Chander See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Difference between configuring data source in persistence.xml and in spring configuration files

I've seen (and done) data source configuration in two ways (the code below is just for demo): 1) configuration ... 's just a matter of taste? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Why is Throwable.fillInStackTrace() method public? Why would someone use it?

I'm curious why is method fillInStackTrace of java.lang.Throwable public? This method replaces original stack trace ... there any sense behind? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Non-final methods in a final class

My question is pretty simple: Does the compiler treat all the methods in a final class as being final themselves ... asking. Thanks in advance. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Best way to consume RPC/encoded webservice?

I need to consume old-school RPC/encoded WSDL webservice for my backend. At first I tried to use Apache CXF and JAX ... do and how to solve it. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - How to get properly current date and time in Joda-Time?

How to get properly actual date and time in Joda Time? By properly I mean time in my country. I read official ... +1 (Prague - Czech Republic)? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Why is hashCode slower than a similar method?

Normally, Java optimizes the virtual calls based on the number of implementations encountered on a given call ... optimization chance #2? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Spring AOP - why do i need aspectjweaver?

i wrote a very simple Aspect with Spring AOP. It works, but i have some problems ... .weaver.reflect.ReflectionWorld$ReflectionWorldException See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - How to open a huge excel file efficiently

I have a 150MB one-sheet excel file that takes about 7 minutes to open on a very powerful machine using the following ... , and number (col 11). See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Jackson: Serialize and deserialize enum values as integers

Consider the following enum and class: public enum State { OFF, ON, UNKNOWN } public class Machine { String name; ... make it behave this way? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - How to stop and resume Observable.interval emiting ticks

This will emit a tick every 5 seconds. Observable.interval(5, TimeUnit.SECONDS, Schedulers.io()) .subscribe( ... the emiting "gracefully"? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - What's the difference between Collections.unmodifiableSet() and ImmutableSet of Guava?

JavaDoc of ImmutableSet says: Unlike Collections.unmodifiableSet, which is a view of a separate collection that can ... Could anyone explain it? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - How to make a boolean variable switch between true and false every time a method is invoked?

I am trying to write a method that when invoked, changes a boolean variable to true, and when invoked again, ... to true and then false again. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Is there an invisible character that is not regarded as whitespace?

I am working with an existing framework where I have to set a certain attribute to blank if some conditions are ... know if it's possible. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Get Spring Security Principal in JSP EL expression

I am using Spring MVC and Spring Security version 3.0.6.RELEASE. What is the easiest way to get the user name in ... a cleaner way to do this... See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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144 views

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java - Why can we not use default methods in lambda expressions?

I was reading this tutorial on Java 8 where the writer showed the code: interface Formula { double calculate( ... having one abstract method. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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302 views

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java - Collections.unmodifiableList and defensive copy

If I write List<Integer> a1 = Arrays.asList(1, 2, 3); List<Integer> a2 = Collections.unmodifiableList(a1 ... defensive copy of that collection? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Is using the Class instance as a Map key a best practice?

I have read somewhere that using the class instances as below is not a good idea as they might cause memory leaks ... (String.class,"Test obj"); See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Android - Expected Resource of type ID

I have this code final static int TITLE_ID = 1; final static int REVIEW_ID = 2; Now, I want to create a new ... it gives me an error. Any idea? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Actions in onActivityResult and "Error Can not perform this action after onSaveInstanceState"

Implementing an app where the user can log in I have the following situation: If the user is logged in ... (Activity.RESULT_OK); finish(); See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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261 views

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java - Exception handling try catch inside catch

I recently came across code written by a fellow programmer in which he had a try-catch statement inside a catch! ... I found this equally bad. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Where should I put my JUnit tests?

I've got 2 questions about organising Unit tests. Do I have to put test to the same package as tested class, ... tests, or put them together? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - How to generate a unique hash code for string input in android...?

I wanted to generate a unique hash code for a string in put in android. Is there any predefined library is there or ... a link or a code stuff. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Android Unit Tests with Dagger 2

I have an Android app that uses Dagger 2 for dependency injection. I am also using the latest gradle build tools ... mock(Random.class); } } See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - Using ConfigurationProperties to fill Map in generic way

I'm wondering, if there is a generic way to fill a map with properties you just know the prefix. ... in the environment? Thanks Hansjoerg See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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372 views

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java - Detach an entity from JPA/EJB3 persistence context

What would be the easiest way to detach a specific JPA Entity Bean that was acquired through an EntityManager. ... to exclude specific objects. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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156 views

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java - What is 'Facet' in JavaEE?

I wonder not only what is Facet but also what is Facet 'in physical level' (as I understand it's not a separate ... that and why do we need it? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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java - How to check whether input value is integer or float?

How to check whether input value is integer or float? Suppose 312/100=3.12 Here i need check whether 3.12 ... , without any decimal place value. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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