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HashMap and int as key
...lt;Integer, MyObject> myMap = new HashMap<Integer, MyObject>();
Java will automatically autobox your int primitive values to Integer objects.
Read more about autoboxing from Oracle Java documentations.
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What does “var FOO = FOO || {}” (assign a variable or an empty object to that variable) mean in Java
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i like to say it's the #ifndef/#define for javascript :)
– Darren Kopp
Jun 22 '11 at 17:15
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How can I count occurrences with groupBy?
...h each group... and then Collectors.counting() to do the counting:
import java.util.*;
import java.util.stream.*;
class Test {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("Hello");
list.add("Hello");
list...
R: += (plus equals) and ++ (plus plus) equivalent from c++/c#/java, etc.?
Does R have a concept of += (plus equals) or ++ (plus plus) as c++/c#/others do?
8 Answers
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Missing return statement in a non-void method compiles
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The Java compiler is smart enough to find the unreachable code ( the code after while loop)
and since its unreachable, there is no point in adding a return statement there (after while ends)
same goes with conditional if
publi...
Properly removing an Integer from a List
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Java always calls the method that best suits your argument. Auto boxing and implicit upcasting is only performed if there's no method which can be called without casting / auto boxing.
The List interface specifies two remove...
Difference between matches() and find() in Java Regex
... {
Pattern p = Pattern.compile("\\d");
String candidate = "Java123";
Matcher m = p.matcher(candidate);
if (m != null){
System.out.println(m.find());//true
System.out.println(m.matches());//false
}
}
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What is the difference between compare() and compareTo()?
What is the difference between Java's compare() and compareTo() methods? Do those methods give same answer?
16 Answers
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Converting BigDecimal to Integer
...red Oct 28 '10 at 14:01
willcodejavaforfoodwillcodejavaforfood
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Check if a value exists in ArrayList
... HashSet than an ArrayList when you are checking for existence of a value.
Java docs for HashSet says: "This class offers constant time performance for the basic operations (add, remove, contains and size)"
ArrayList.contains() might have to iterate the whole list to find the instance you are looki...