=================================
Topic07_Code01_GenericMethod preparation
=================================
public class Main {
	public static void main(String[] args) {
		printTwice("hello");
	}

	public static void printTwice(String x) {
		System.out.println(x);
		System.out.println(x);
	}
}

//		printTwice(1234);
//		printTwice(4.0 / 3);

=================================
Topic07_Code01_GenericMethod
=================================
public class Main {
	public static <T> void printTwice(T x) {
		System.out.println(x);
		System.out.println(x);
	}

	public static void main(String[] args) {
		printTwice("hello");
		printTwice(1234);
		printTwice(4.0 / 3);
	}
}

// public static <T> void printTwiceB(T x)
// {
// T y=x;
// System.out.println(y);
// System.out.println(y);
// }


=================================
Topic07_Code02_GenericClass (preparation)
================================= 
import java.io.*;
import java.util.*;

class Pair {
	private String first;
	private String second;

	public Pair() {
	} // first and second automatically initialized as null

	public Pair(String x1, String x2) {
		first = x1;
		second = x2;
	}

	@Override
	public String toString() {
		return "(1)" + first + " (2)" + second;
	}
}

public class Main {

	public static void main(String[] args) {
		Pair p0 = new Pair();
		Pair p1 = new Pair("hello", "cheers");
        
		System.out.println(p0);
		System.out.println(p1);

		// Pair p2 = new Pair(true, false);
		// Pair p3 = new Pair(123, 456);
		// Pair p4 = new Pair(12.3, 45.6);
		// Pair p5 = new Pair(123, "cheers");
		// System.out.println(p2);
		// System.out.println(p3);
		// System.out.println(p4);
		// System.out.println(p5);
	}
}

=================================
Topic07_Code02_GenericClass
=================================

class Pair<T> {
    public T first;
    public T second;

    public Pair() {
    }

    public Pair(T x1, T x2) {
        first = x1;
        second = x2;
    }

    @Override
    public String toString() {
        return "(1)" + first + " (2)" + second;
    }
}

public class Main {
    public static void main(String[] args) {

        Pair<String> p0 = new Pair<String>();
        Pair<String> p1 = new Pair<String>("hello", "cheers");
        Pair<Object> p5 = new Pair<Object>(123, "cheers");

        System.out.println(p0); // (1)null (2)null
        System.out.println(p1); // (1)hello (2)cheers
        System.out.println(p5); // (1)123 (2)cheers

        System.out.println(p5.first.getClass().toString());
        System.out.println(p5.second.getClass().toString());
    }
}


=================================
Topic07_Code02_GenericClass
=================================
class Pair<T> {
	private T first;
	private T second;

	public Pair() {
	} // first and second automatically initialized as null

	public Pair(T x1, T x2) {
		first = x1;
		second = x2;
	}

	@Override
	public String toString() {
		return "(1)" + first + " (2)" + second;
	}
}

public class Main {
	public static void main(String[] args) {
		Pair<String> p0 = new Pair<String>();
		Pair<String> p1 = new Pair<String>("hello", "cheers");
		Pair<Boolean> p2 = new Pair<Boolean>(true, false);
		Pair<Integer> p3 = new Pair<Integer>(123, 456);
		Pair<Number> p4 = new Pair<Number>(123, 456);
		Pair<Object> p5 = new Pair<Object>(123, "cheers");
		
        //Error: The constructor Pair<Integer>(int, String) is undefined
        // Pair<Integer> p6 = new Pair<Integer>(123,"cheers"); 
        
		System.out.println(p0);
		System.out.println(p1);
		System.out.println(p2);
		System.out.println(p3);
		System.out.println(p4);
		System.out.println(p5);
	}
}

// (1)null (2)null
// (1)hello (2)cheers
// (1)true (2)false
// (1)123 (2)456
// (1)123 (2)456
// (1)123 (2)cheers


=================================
Topic07_Code03_ArrayListAndSort
=================================

import java.util.ArrayList;
import java.util.Collections;

public class Main {
    public static void main(String[] args) {
        ArrayList<Integer> arrlist = new ArrayList<>();
        arrlist.add(1234);
        arrlist.add(8899);
        arrlist.add(36);
        Collections.sort(arrlist);

        System.out.println(arrlist); // Output: [36, 1234, 8899]
    }
}

=================================
Topic07_Code03_ArrayAndSort
=================================
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Collections;

public class Main {
    public static void main(String[] args) {
        ArrayList<Integer> arrlist = new ArrayList<>();
        arrlist.add(1234);
        arrlist.add(8899);
        arrlist.add(36);
        Collections.sort(arrlist);

        Object[] a = arrlist.toArray();
        System.out.println(Arrays.toString(a)); // Output: [36, 1234, 8899]

        List<Integer> b = arrlist.subList(0, 2);
        System.out.println(b); // Output: [36, 1234]
    }
}


=================================
Topic07_Code04_DiamondSyntax
=================================

class Pair<T> {
    private T first;
    private T second;

    public Pair() {
    } // first and second automatically initialized as null

    public Pair(T x1, T x2) {
        first = x1;
        second = x2;
    }

    @Override
    public String toString() {
        return "(1)" + first + " (2)" + second;
    }
}

public class Main {
    public static void main(String[] args) {
        Pair<String> p0 = new Pair<>();
        Pair<String> p1 = new Pair<>("hello", "cheers");
        Pair<Boolean> p2 = new Pair<>(true, false);
        Pair<Integer> p3 = new Pair<>(123, 456);
        Pair<Number> p4 = new Pair<>(123, 456); 
        Pair<Object> p5 = new Pair<>(123, "cheers"); 

        System.out.println(p0);
        System.out.println(p1);
        System.out.println(p2);
        System.out.println(p3);
        System.out.println(p4);
        System.out.println(p5);
    }
}



=================================
Topic07_Code05_MobileDevice
=================================

class Smartphone {
}

class Pager {
}

class TabletPC {
}

class MobileDevice<T> {
    private static int count = 0;

    MobileDevice() {
        count++;
        System.out.println(count);
    }
    // ...
}

public class Main {
    public static void main(String[] args) {
        MobileDevice<Smartphone> phone = new MobileDevice<>();
        MobileDevice<Pager> pager = new MobileDevice<>();
        MobileDevice<TabletPC> pc = new MobileDevice<>();
    }
}


=================================
Topic07_Code06_Pitfalls
=================================

import java.util.*;
class Smartphone {} class Pager {} class TabletPC {}


class MobileDevice<T> {
	private static int count = 0;

	MobileDevice() {
		count++;
		System.out.println(count);
	}

	public static <T> void append_arbitary(ArrayList<T> list) {
		T one = null;
		// one = new T(); // compile-time error
		list.add(one);
	}

	public static <T> void appendOne(ArrayList<T> list, T one) {
		list.add(one);
	}
}

public class Main {
	public static void main(String[] args) {
		MobileDevice<Smartphone> phone = new MobileDevice<>();
		MobileDevice<Pager> pager = new MobileDevice<>();
		MobileDevice<TabletPC> pc = new MobileDevice<>();
	}
}


=================================
Topic07_Code06_Pitfalls
=================================

class Smartphone {
}

class Pager {
}

class TabletPC {
}

class MobileDevice<T> {
	private static int count=0;  

	MobileDevice() {count++;System.out.println(count);} 
}

public class Main {
	// public void print(MobileDevice<Pager> x) {}
	// public void print(MobileDevice<Smartphone> x) {}
	
	public static void main(String[] args) {
		MobileDevice<Smartphone> phone = new MobileDevice<>();
		MobileDevice<Pager> pager = new MobileDevice<>();
		MobileDevice<TabletPC> pc = new MobileDevice<>();
	}
}

=================================
Topic07_Code09_PairTypeErased
=================================

//Topic07 Generic Programming Slide 10

class Pair {
    public Object first;
    public Object second;

    public Pair() {
    }

    public Pair(Object first, Object second) {
        this.first = first;
        this.second = second;
    }

    @Override
    public String toString() {
        return "(1)" + first + " (2)" + second;
    }
}

public class Main {
    public static void main(String[] args) {

        Pair p0 = new Pair();
        Pair p1 = new Pair("hello", "cheers");
        Pair p5 = new Pair(123, "cheers");

        System.out.println(p0); // (1)null (2)null
        System.out.println(p1); // (1)hello (2)cheers
        System.out.println(p5); // (1)123 (2)cheers

        System.out.println(p5.first.getClass().toString());
        System.out.println(p5.second.getClass().toString());
    }
}


=================================
^_^
=================================
import java.util.*;

class Student {}
class Teacher {}

public class Main {
	static ArrayList<Teacher> arrT = new ArrayList<>();
	static ArrayList<Student> arrS = new ArrayList<>();	
	
	private static void lowerSchoolFees(ArrayList<Student> arr) {}

	private static void raiseTeacherSalary(ArrayList<Teacher> arr) {}

	public static void main(String[] args) {
		//..
		raiseTeacherSalary(arrT);
		lowerSchoolFees(arrS);	
	}
}



=================================
Topic07_Code10_TestingRawTypes
=================================

class Box<T> {
    private T t;

    public void set(T t) {
        this.t = t;
    }

    @Override
    public String toString() {
        return "This is " + t;
    }
    // ...
}

public class Main {
    public static void main(String[] args) {
        Box<Integer> a = new Box<>();
        a.set(3);
        System.out.println(a);

        Box b = new Box();  // warning <== "raw type"
        b.set(4.0 / 3);
        System.out.println(b);

        // Box<String> b = new Box<>(); 
        // b.set(4.0 / 3);
        // System.out.println(b);
}


=================================
Topic07_Code
=================================
class Pair<T> {
  public T first;
  public T second;

  public Pair() {
  }

  public Pair(T x1, T x2) {
    first = x1;
    second = x2;
  }

  @Override
  public String toString() {
    return "(1) " + first + ", (2) " + second;
  }
}

public class Main {
  public static void main(String[] args) {
    Pair<Integer> p0 = new Pair<>(100, 200);
    // Pair<Number> p1 = p0;
    // Pair<Number> p2 = (Pair<Number>)p0;
    Pair<? extends Number> p3 = (Pair<? extends Number>) p0;
    Pair<? extends Number> p4 = p0;

    System.out.println(p3);
    System.out.println(p4);
  }
}


=================================
Topic07_Code11_Pair2TypeParameters
=================================

class TwoTypePair<T1, T2> {
    private T1 first;
    private T2 second;

    public TwoTypePair(T1 firstItem, T2 secondItem) {
        first = firstItem;
        second = secondItem;
    }

    public void setFirst(T1 newFirst) {
        first = newFirst;
    }

    public void setSecond(T2 newSecond) {
        second = newSecond;
    }

    public T1 getFirst() {
        return first;
    }

    public T2 getSecond() {
        return second;
    }

    public String toString() {
        return ("first: " + first.toString() + "\n" + "second: " + second.toString());
    }

    public boolean equals(Object otherObject) {
        if (otherObject == null)
            return false;
        else if (getClass() != otherObject.getClass())
            return false;
        else {
            TwoTypePair<T1, T2> otherPair = (TwoTypePair<T1, T2>) otherObject;
            return (first.equals(otherPair.first) && second.equals(otherPair.second));
        }
    }
}

public class Main {
    public static void main(String[] args) {
        TwoTypePair<String, Integer> x1 = new TwoTypePair<>("USD", 123);
        TwoTypePair<String, Integer> x2 = new TwoTypePair<>("USD", 456);
        TwoTypePair<String, Integer> x3 = new TwoTypePair<>("USD", 123);

        System.out.println(x1.equals(x2));// false
        System.out.println(x1.equals(x3));// true
    }
}


=================================
Topic07_Code12_Inheritance
=================================

class C0 {
}

class C1<T> extends C0 {
}

class C2<T> extends C1<T> {

}

class C3<T> extends C1<String> {
}

class Pair<T> {
    private T first;
    private T second;

    public Pair(T x1, T x2) {
        first = x1;
        second = x2;
    }

    public <S> void display(S head1, S head2) {
        System.out.println("(" + head1 + ")" + first + ", (" + head2 + ")" + second);
    }

    public <S extends Comparable<S>> void showHigherCost(S cost1, S cost2) {
        S higher = cost1.compareTo(cost2) > 0 ? cost1 : cost2;
        if (higher == cost1)
            System.out.printf("More expensive: " + first + " $" + higher);
        else
            System.out.println("More expensive: " + second + " $" + higher);
    }
}

public class Main {
    public static void main(String[] args) {
        Pair<String> p = new Pair<String>("Orange", "Pear");
        p.<String>display("a", "b");
        p.<Integer>display(1, 2);
        p.<Double>showHigherCost(10.0, 20.0);

        p.display("a", "b");
        p.display(1, 2);
        p.showHigherCost(10.0, 20.0);
    }
}

/*
(a)Orange, (b)Pear
(1)Orange, (2)Pear
More expensive: Pear $20.0
(a)Orange, (b)Pear
(1)Orange, (2)Pear
More expensive: Pear $20.0
*/


=================================
Topic07_Code13_GenericClassUnorderedPair
=================================

class Pair<T> {
    private T first;
    private T second;

    public Pair(T x1, T x2) {
        first = x1;
        second = x2;
    }

    @Override
    public String toString() {
        return "(1)" + first + " (2)" + second;
    }

    public T getFirst() {
        return first;
    }

    public T getSecond() {
        return second;
    }
}

class UnorderedPair<T> extends Pair<T> {
    public UnorderedPair(T firstItem, T secondItem) {
        super(firstItem, secondItem);
    }

    public boolean equals(Object otherObject) {
        if (otherObject == null)
            return false;
        else if (getClass() != otherObject.getClass())
            return false;
        else {
            UnorderedPair<T> otherPair = (UnorderedPair<T>) otherObject;
            return 
                ( getFirst().equals(otherPair.getFirst()) && 
                  getSecond().equals(otherPair.getSecond()) ) || 
                ( getFirst().equals(otherPair.getSecond()) && 
                  getSecond().equals(otherPair.getFirst()));
        }
    }
}

public class Main {
    public static void main(String[] args) {
        UnorderedPair<String> x1 = new UnorderedPair<>("ABC", "DEF");
        UnorderedPair<String> x2 = new UnorderedPair<>("DEF", "ABC");
        UnorderedPair<String> x3 = new UnorderedPair<>("DEF", "AAA");
        System.out.println(x1.equals(x2));// true
        System.out.println(x1.equals(x3));// false
    }
}

=================================