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java.util is a class in java containing several convinient methods and such. It includes, but is not limited, to some array manipulations tools, a collection framework and date and time tools.
Classes[]
Arrays[]
Arrays is a static class containing helper methods that may be useful when using arrays.
Sort[]
java.util.Arrays.sort can be used to sort arrays.
java.util.Arrays.sort(a);
Here a is the name of the array to sort.
Strings or chars will be sorted in alphabetical order, while any number datatypes will be sorted in ascending numerical order.
Scanner[]
Scanners can be used to easily collect user input without using BufferedReaders.
import java.util.Scanner; Scanner scan = new Scanner(System.in); String operat = scan.next(); //Change "String" to correct type.
Here used with int:
import java.util.Scanner; Scanner scan = new Scanner(System.in); int operat = scan.nextInt(); //Notice how "scan.next();" changed to "scan.nextInt();"
Collections[]
Collections is a static class containing helper methods that may be useful when using a class that implements the Collection interface.
Interfaces[]
List[]
Map[]
Set[]
in the mathematical sense Sets have a number of operations that are not present in the Java implementation. fortunately they are easy to simulate.
Intersection[]
Set setA = new HashSet(); Set setB = new HashSet(); //add elements to sets setA.retainAll(setB);
Complement[]
Set setA = new HashSet(); Set setB = new HashSet(); //add elements to sets setA.removeAll(setB);