java generics

// generic methods public <T> List<T> fromArrayToList(T[] a) { return Arrays.stream(a).collect(Collectors.toList()); } public static <T, G> List<G> fromArrayToList(T[] a, Function<T, G> mapperFunction) { return Arrays.stream(a) .map(mapperFunction) .collect(Collectors.toList()); } // bounded generics public <T extends Number> List<T> fromArrayToList(T[] a) { ... } //multiple bounds <T extends Number & Comparable> // upper bound wildcards public static void paintAllBuildings(List<? extends Building> buildings) { ... } // lower bound wildcard <? super T>

public class Tuple <T> { // the T is a placeholder for any datatype public T leftValue; public T rightValue; public Tuple(T leftValue, T rightValue){ // again, T is being used as a placeholder for any type this.leftValue = leftValue; this.rightValue = rightValue; } public class Program{ public static void main (String args){ // And upon using Tuples we can fill in the T from the Tuple class with actual datatypes Tuple <int> intTuple = new Tuple <int>(5, 500) Tuple <String> stringTuple = new Tuple <String> ("Hello", "World") // we can even put Tuples inside of Tuples! Tuple<Tuple<int>> metaIntTuple = new Tuple <Tuple <int>> (intTuple, new Tuple <int> (456, 0)); } }

Java Generic Type Naming convention helps us understanding code easily and having a naming convention is one of the best practices of Java programming language. So generics also comes with its own naming conventions. Usually, type parameter names are single, uppercase letters to make it easily distinguishable from java variables. The most commonly used type parameter names are: E – Element (used extensively by the Java Collections Framework, for example ArrayList, Set etc.) K – Key (Used in Map) N – Number T – Type V – Value (Used in Map) S,U,V etc. – 2nd, 3rd, 4th types

generics in java

import java.util.Scanner;
import reader.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        String filePath = scanner.nextLine().trim();
        System.out.println("The file path is " + filePath);
        String type = filePath.substring(filePath.lastIndexOf('.') + 1).replaceAll("\\W", "");
        System.out.println("The reader type is " + type);
        AbstractReaderService reader = getReaderService(type);
        // reader.read(filePath);
        // reader.printContent();

    }

    private static AbstractReaderService getReaderService (String type) throws Exceptions.TypeNotFoundException {
        switch (type) {
            case "txt": return new TxtReaderService();
            case "json": return new JsonReaderService();
            default: throw new Exceptions().new TypeNotFoundException("There is no \"" + type + "\" type of reader.");
        }
    }
}

Posted by: Guest on August-10-2021

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