Problem Solving # 9: ArrayList, Collections and More

1. Problem Solving # 9: ArrayList, Collections and More ICS201-071

2. Outline • Review of Key Topics • Problem 1: Using ArrayList Class … • Problem 2: Iterators and ListIterators • Problem 3: Applications of ArrayList …. • Problem 4: Java Collections … • Problem 5: Java Generics …

3. ArrayList Class: Tips import java.util.ArrayList;public class MyArrayList1 {public static void main(String[] args) {    Seller sel = new Seller();    Buyer buy = new Buyer();    // declare an array list of type Seller    ArrayList<Seller> list = new ArrayList<Seller>();    list.add(sel); // add object of type Seller which is permisible    list.add(buy);  // this statement will give an error   }} // Classes Seller and Buyer are supposed defined earlier….

4. ArrayList Class: Tips (Cont’d) import java.util.ArrayList;public class MyArrayList2 {public static void main(String[] args) {      // declare an array list of Integer    ArrayList<Integer> list = new ArrayList<Integer>();    list.add(5);  // Automatic boxing    list.add(new Integer(6));   int value = list.get(1); System.out.println(value);   }}

5. ArrayList Class: Tips (Cont’d) import java.util.*;public class ArrayListGenericDemo {public static void main(String[] args) {    ArrayList<String> data = new ArrayList<String>();    data.add("hello");    data.add("goodbye");    // data.add(new Date()); This won't compile!    Iterator<String> it = data.iterator();while (it.hasNext()) {      String s = it.next();      System.out.println(s);    }  }}

6. Java Generics: Tips class GenCons {private double val;  <T extends Number> GenCons(T arg) {    val = arg.doubleValue();  }void showval() {    System.out.println("val: " + val);  }}public class GenConsDemo {public static void main(String args[]) {    GenCons test = new GenCons(100);    GenCons test2 = new GenCons(123.5F);    test.showval();    test2.showval();  }}

7. Java Generics: Tips (Con’d) public class GenMethDemo {    // Determine if an object is in an array. static <T, V extends T> boolean isIn(T x, V[] y) { for(int i=0; i < y.length; i++) if(x.equals(y[i])) return true; return false;   } public static void main(String args[]) {      // Use isIn() on Integers.     Integer nums[] = { 1, 2, 3, 4, 5 }; if(isIn(2, nums))       System.out.println("2 is in nums"); if(!isIn(7, nums))       System.out.println("7 is not in nums");     System.out.println();     // Use isIn() on Strings.     String strs[] = { "one", "two", "three",                       "four", "five" }; if(isIn("two", strs))       System.out.println("two is in strs"); if(!isIn("seven", strs))       System.out.println("seven is not in strs");     // Opps! Won't compile! Types must be compatible. //    if(isIn("two", nums)) //      System.out.println("two is in strs");   }  }

8. HashSet: Tips import java.util.*; public class HashSet1 { public static void main( String[] args ) { HashSet<Integer> set = new HashSet<Integer>(); set.add( new Integer( 6 ) ); set.add( new Integer( 1 ) ); set.add( new Integer( 4 ) ); System.out.println( set ); System.out.println(); System.out.println( "Show that duplicates cannot be added." ); set.add( new Integer( 8 ) ); System.out.println( "New contents are " + set ); boolean value = set.add( new Integer( 4 ) ); if(value) System.out.println(" A duplicate value has been added!"); else System.out.println(" A duplicate value can NOT be added!"); System.out.println( "New contents are " + set ); } }

9. Form Groups of 3 Students and Work on the Following Problem

10. Problem 1: Using ArrayList Class to store Student data. Student data: id, name, gpa and major

11. Problem 1 … a) Define the Student class b) Write the test class c) Search for a specific Student record

12. Solution

13. Problem 2 … • Search for a specific Student record using an iterator • Remove all the duplicate copies of a specific Student record using an iterator

14. Solution

15. Problem 3 Swapping a list of ArrayList elements: a) Using the for-each loop c) Using iterators (….)

16. Solution

17. Problem 4 Consider the following code…

18. Problem 4 import java.util.*;public class CollectionTest {public static void main(String [] args) {       System.out.println( "Collection Example!\n" ); int size;    // Create a collection          HashSet <String>collection = new HashSet <String>();    String str1 = "Yellow", str2 = "White", str3 = "Green", str4 = "Blue";      Iterator iterator;    //Adding data in the collection    collection.add(str1);        collection.add(str2);       collection.add(str3);       collection.add(str4);    System.out.print("Collection data: ");      //Create a iterator    iterator = collection.iterator();     while (iterator.hasNext()){      System.out.print(iterator.next() + " ");      }    System.out.println();    // Get size of a collection    size = collection.size();if (collection.isEmpty()){      System.out.println("Collection is empty");    }else{      System.out.println( "Collection size: " + size);    }    System.out.println(); // Remove specific data          collection.remove(str2);    System.out.println("After removing [" + str2 + "]\n");    System.out.print("Now collection data: ");    iterator = collection.iterator();     while (iterator.hasNext()){      System.out.print(iterator.next() + " ");      }    System.out.println();    size = collection.size();    System.out.println("Collection size: " + size + "\n");    //Collection empty    collection.clear();    size = collection.size();if (collection.isEmpty()){      System.out.println("Collection is empty");    }else{      System.out.println( "Collection size: " + size);    }  }}

19. Problem 5 • Define a generic class as follows: class Gen<T> {  T ob; // declare an object of type T  Gen(T o) {    ob = o;  }  T getob() {return ob;  }void showType() {    System.out.println("Type of T is " + ob.getClass().getName());  }}

20. Problem 5 (Cont’d) public class GenDemo {public static void main(String args[]) {    Gen<Integer> iOb;    iOb = new Gen<Integer>(88);    iOb.showType();int v = iOb.getob();    System.out.println("value: " + v);    System.out.println();    Gen<String> strOb = new Gen<String>("Generics Test");    strOb.showType();    String str = strOb.getob();    System.out.println("value: " + str);  }}