I’m looking at some open source Java projects to get into Java and notice a lot of them have some sort of ‘constants’ interface. For instance, processing.org has an interface called PConstants.java, and most other core classes implement this interface. The interface is riddled with static me…
Tag: java
How do I set environment variables from Java?
How do I set environment variables from Java? I see that I can do this for subprocesses using ProcessBuilder. I have several subprocesses to start, though, so I’d rather modify the current process’s environment and let the subprocesses inherit it. There’s a System.getenv(String) for getting …
How do I read / convert an InputStream into a String in Java?
If you have a java.io.InputStream object, how should you process that object and produce a String? Suppose I have an InputStream that contains text data, and I want to convert it to a String, so for example I can write that to a log file. What is the easiest way to take the InputStream and convert it to a Str…
A range intersection algorithm better than O(n)?
Range intersection is a simple, but non-trivial problem. Its has been answered twice already: Find number range intersection Comparing date ranges The first solutions is O(n) and the second solution is for a database (which is less than O(n) of course). I have the same problem, but for a large n and I am not …
Why does Java’s hashCode() in String use 31 as a multiplier?
Per the Java documentation, the hash code for a String object is computed as: using int arithmetic, where s[i] is the ith character of the string, n is the length of the string, and ^ indicates exponentiation. Why is 31 used as a multiplier? I understand that the multiplier should be a relatively large prime …
Inserting a node into a linked list in constant-time?
I’m working on an assignment that is telling me to assume that I have a singly linked list with a header and tail nodes. It wants me to insert an item y before position p. Can anybody please look over my code and tell me if I’m on the right track? If not, can you provide me with any tips
Output RFC 3339 Timestamp in Java
I want to output a timestamp with a PST offset (e.g., 2008-11-13T13:23:30-08:00). java.util.SimpleDateFormat does not seem to output timezone offsets in the hour:minute format, it excludes the colon. Is there a simple way to get that timestamp in Java? Also, SimpleDateFormat cannot properly parse the example …
What is meant by immutable?
What exactly does immutable mean – that is, what are the consequences of an object being mutable or immutable? In particular, why are Java’s Strings immutable? My understanding is that the StringBuilder type is something like a mutable equivalent to String. When would I use StringBuilder rather th…
How do I count the number of occurrences of a char in a String?
I have the string I want to count the occurrences of ‘.’ in an idiomatic way, preferably a one-liner. (Previously I had expressed this constraint as “without a loop”, in case you’re wondering why everyone’s trying to answer without using a loop). Answer My ‘idiomatic …
Can java’s assert statement allow you to specify a message?
Seems likes it might be useful to have the assert display a message when an assertion fails. Currently an AssertionError gets thrown, can you specify a custom message for it? Can you show an example mechanism for doing this (other than creating your own exception type and throwing it)? Answer You certainly ca…