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Commit 2238092

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rfadatare
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Java Generics Examples
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‎pom.xml‎

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.javaguides.generics</groupId>
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<artifactId>java-generics-guide</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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</project>
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package com.javaguides.generics.classes;
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public class GenType<T> {
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private T t;
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public T get() {
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return this.t;
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}
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public void set(T t1) {
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this.t = t1;
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}
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public static void main(String args[]) {
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// Generic type with Integer Type
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GenType<Integer> type = new GenType<>();
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type.set(10); // valid
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System.out.println(type.get());
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// Generic type with String Type
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GenType<String> typeStr = new GenType<>();
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typeStr.set("String");
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System.out.println(typeStr.get());
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// Generic type with Custom Student Type
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GenType<Student> genericType = new GenType<>();
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Student student = new Student();
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student.setName("Ramesh");
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genericType.set(student);
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System.out.println(genericType.get());
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@SuppressWarnings("rawtypes")
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GenType type1 = new GenType(); // raw type
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type1.set("Ramesh"); // valid
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type1.set(10); // valid and autoboxing support
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System.out.println("Raw Type :" + type1.get());
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}
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}
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class Student{
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private String name;
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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}
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package com.javaguides.generics.classes;
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public class GenericClass<T extends A> {
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private T t;
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public GenericClass(T t){
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this.t = t;
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}
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public void doRunTest() {
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this.t.displayClass();
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}
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public static void main(String[] args) {
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// Creating object of sub class C and
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// passing it to Bound as a type parameter.
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GenericClass<C> bec = new GenericClass<C>(new C());
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bec.doRunTest();
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// Creating object of sub class B and
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// passing it to Bound as a type parameter.
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GenericClass<B> beb = new GenericClass<B>(new B());
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beb.doRunTest();
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// similarly passing super class A
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GenericClass<A> bea = new GenericClass<A>(new A());
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bea.doRunTest();
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}
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}
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class A {
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public void displayClass() {
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System.out.println("Inside super class A");
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}
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}
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class B extends A {
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public void displayClass() {
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System.out.println("Inside sub class B");
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}
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}
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class C extends A {
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public void displayClass() {
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System.out.println("Inside sub class C");
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}
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}
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package com.javaguides.generics.classes;
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/**
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* Generic class example. Create GenericFactory<T> to get any type of instance.
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* @author javaguides.net
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*
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*/
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public class GenericClassExample {
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public static void main(String[] args) throws IllegalAccessException, InstantiationException {
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GenericFactory<ProductA> factory = new GenericFactory<ProductA>(ProductA.class);
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ProductA productA = factory.createInstance();
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System.out.println(productA.getProductName());
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GenericFactory<ProductB> factoryB = new GenericFactory<ProductB>(ProductB.class);
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ProductB productB = factoryB.createInstance();
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System.out.println(productB.getProductName());
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GenericFactory<ProductC> factoryC = new GenericFactory<ProductC>(ProductC.class);
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ProductC productC = factoryC.createInstance();
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System.out.println(productC.getProductName());
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}
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}
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class ProductA {
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public String getProductName() {
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return "Product A";
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}
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}
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class ProductB {
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public String getProductName() {
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return "Product B";
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}
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}
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class ProductC {
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public String getProductName() {
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return "Product C";
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}
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}
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class GenericFactory<T> {
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Class theClass = null;
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public GenericFactory(Class theClass) {
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this.theClass = theClass;
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}
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public T createInstance() throws IllegalAccessException, InstantiationException {
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return (T) this.theClass.newInstance();
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}
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}
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package com.javaguides.generics.classes;
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/**
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* Generic interface example to find min and max of array.
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* @author javaguides.net
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*
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*/
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public class GenericInterfaceExample {
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public static void main(String args[]) {
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Integer intOfArray[] = { 3, 6, 2, 8, 6 };
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Character charOfArray[] = { 'A', 'r', 'V', 'w' };
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String strOfArray[] = {"abc", "xyz", "pqr"};
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MinMaxImpl<Integer> intMinMax = new MinMaxImpl<Integer>(intOfArray);
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MinMaxImpl<Character> charMinMax = new MinMaxImpl<Character>(charOfArray);
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MinMaxImpl<String> strMinMax = new MinMaxImpl<String>(strOfArray);
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System.out.println("Max value in intOfArray: " + intMinMax.max());
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System.out.println("Min value in intOfArray: " + intMinMax.min());
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System.out.println("Max value in charOfArray: " + charMinMax.max());
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System.out.println("Min value in charOfArray: " + charMinMax.min());
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System.out.println("Max value in strOfArray: " + strMinMax.max());
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System.out.println("Min value in strOfArray: " + strMinMax.min());
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}
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}
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interface MinMax<T extends Comparable<T>> {
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T min();
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T max();
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}
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class MinMaxImpl<T extends Comparable<T>> implements MinMax<T> {
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T[] vals;
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MinMaxImpl(T[] o) {
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vals = o;
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}
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public T min() {
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T v = vals[0];
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for (int i = 1; i < vals.length; i++) {
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if (vals[i].compareTo(v) < 0) {
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v = vals[i];
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}
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}
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return v;
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}
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public T max() {
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T v = vals[0];
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for (int i = 1; i < vals.length; i++) {
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if (vals[i].compareTo(v) > 0) {
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v = vals[i];
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}
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}
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return v;
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}
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}
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package com.javaguides.generics.classes;
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import java.util.Arrays;
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import java.util.List;
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import java.util.function.Function;
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import java.util.stream.Collectors;
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/**
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* Generic methods example to convert array to list.
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* @author javaguides.net
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*
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*/
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public class GenericMethodsExamples {
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// definition of a generic method
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public static <T> List<T> fromArrayToList(T[] a) {
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return Arrays.stream(a).collect(Collectors.toList());
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}
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// definition of a generic method
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public static <T, G> List<G> fromArrayToList(T[] a, Function<T, G> mapperFunction) {
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return Arrays.stream(a).map(mapperFunction).collect(Collectors.toList());
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}
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// example of a generic method that has Number as an upper bound for T
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public static <T extends Number> List<T> fromArrayToListWithUpperBound(T[] a) {
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return Arrays.stream(a).collect(Collectors.toList());
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}
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public static void main(String[] args) {
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// testing the generic method with Integer
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Integer[] intArray = { 1, 2, 3, 4, 5 };
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List<Integer> list = fromArrayToList(intArray);
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list.forEach(element -> System.out.println(element));
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// testing the generic method with String
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String[] stringArray = { "hello1", "hello2", "hello3", "hello4", "hello5" };
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List<String> strList = fromArrayToList(stringArray);
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strList.forEach(element -> System.out.println(element));
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// testing the generic method with Integer and String type
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Integer[] intArr = { 1, 2, 3, 4, 5 };
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List<String> stringList = fromArrayToList(intArr, Object::toString);
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stringList.forEach(element -> System.out.println(element));
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}
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}
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package com.javaguides.generics.classes;
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public class GenericMultipleTypeParametersExample {
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public static void main(String[] args) {
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OrderedPair<String, Integer> p1 = new OrderedPair<>("Even", 8);
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System.out.println(p1.getKey());
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System.out.println(p1.getValue());
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OrderedPair<String, String> p2 = new OrderedPair<>("hello", "world");
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System.out.println(p2.getKey());
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System.out.println(p2.getValue());
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OrderedPair<String, Employee> p3 = new OrderedPair<>("key", new Employee("Ramesh"));
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System.out.println(p3.getKey());
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System.out.println(p3.getValue().getName());
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}
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}
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class Employee{
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private String name;
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Employee(String name){
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this.name = name;
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}
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public String getName(){
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return this.name;
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}
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}
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interface Pair<K, V> {
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public K getKey();
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public V getValue();
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}
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class OrderedPair<K, V> implements Pair<K, V> {
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private K key;
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private V value;
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public OrderedPair(K key, V value) {
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this.key = key;
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this.value = value;
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}
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public K getKey() { return key; }
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public V getValue() { return value; }
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}

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