how to create a generic class in java

java generic type method

// 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>

Posted by: Guest on October-31-2020

Source

List<String> list1 = new ArrayList<String>(); // java 7 ? List<String> list1 = new ArrayList<>(); list1.add("abc"); //list1.add(new Integer(5)); //compiler error for(String str : list1){ //no type casting needed, avoids ClassCastException }

// 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>

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