Answers for "java generic class"

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>

java generics

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 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>

generic class java

public interface Pair<K, V> {
    public K getKey();
    public V getValue();
}

public class OrderedPair<K, V> implements Pair<K, V> {

    private K key;
    private V value;

    public OrderedPair(K key, V value) {
	this.key = key;
	this.value = value;
    }

    public K getKey()	{ return key; }
    public V getValue() { return value; }
}

java generics

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 define a generic class that produces

List list = new ArrayList();
list.add("abc");
list.add(new Integer(5)); //OK

for(Object obj : list){
	//type casting leading to ClassCastException at runtime
    String str=(String) obj; 
}

generic class java

public interface Pair<K, V> {
    public K getKey();
    public V getValue();
}

public class OrderedPair<K, V> implements Pair<K, V> {

    private K key;
    private V value;

    public OrderedPair(K key, V value) {
	this.key = key;
	this.value = value;
    }

    public K getKey()	{ return key; }
    public V getValue() { return value; }
}

java define a generic class that produces

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
}

java define a generic class that produces

List list = new ArrayList();
list.add("abc");
list.add(new Integer(5)); //OK

for(Object obj : list){
	//type casting leading to ClassCastException at runtime
    String str=(String) obj; 
}

java define a generic class that produces

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
}