Basically, you check if an object is an instance of a specific class. You normally use it, when you have a reference or parameter to an object that is of a super class or interface type and need to know whether the actual object has some other type (normally more concrete). Example: Note that if … Read more
There are several differences between HashMap and Hashtable in Java: Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones. Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values. One of HashMap’s subclasses is LinkedHashMap, so in the event that you’d want predictable iteration order (which is insertion order by default), you … Read more
Parameters and local variables are allocated on the stack (with reference types, the object lives on the heap and a variable in the stack references that object on the heap). The stack typically lives at the upper end of your address space and as it is used up it heads towards the bottom of the address space (i.e. towards zero). Your process also … Read more
Nothing. will undergo autoboxing. The compiler replaces it with: You can see this if you decompile your class, e.g. using javap. Decompiles to: So how it is better initialize a variable, considering memory consumption and time complexity? Because they are semantically identical, the memory consumption and time complexity is also identical. Instead, focus on what is actually … Read more
Note that if you need to use i.remove(); in your loop, or access the actual iterator in some way, you cannot use the for ( : ) idiom, since the actual iterator is merely inferred. As was noted by Denis Bueno, this code works for any object that implements the Iterable interface. Note that if … Read more
The n variable was declared in the main method and thus is visible only in the main method, nowhere else, and certainly not inside of the calcNumFactors method. To solve this, give your calcNumFactors method an int parameter which would allow calling methods to pass an int, such as n into the method. and call it like so:
I am experiencing an error while trying to compile Java programs. I am on Windows (this is a Windows-specific problem) and I have the latest JDK installed. I have attempted a solution involving the PATH variable, but the error persists. Console output:
Closed. This question is not reproducible or was caused by typos. It is not currently accepting answers. Want to improve this question? Update the question so it’s on-topic for Stack Overflow. Closed 7 years ago.Improve this question I am experiencing an error while trying to compile Java programs. I am on Windows (this is a Windows-specific problem) and I have the … Read more
Instance variable is the variable declared inside a class, but outside a method: something like: Now this IronMan Class can be instantiated in another class to use these variables. Something like: This is how we use the instance variables. Shameless plug: This example was pulled from this free e-book here here.
The first solution is to use the java.util.Random class: Another solution is using Math.random(): or