Java.utils — code

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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.

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

List

Map

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);