• Arrays

  Multiple values of common type.

  Loop style handling.

final String
      karen = "Karen Smith",
      john = "John Duncan",
      paul = "Paul Jacobs",
      suzanne = "Suzanne Enders",
      peter = "Peter Phillips";  // 10 more to come ...

    System.out.println(karen);
    System.out.println(john);
...

final int[] primes ❶ = new int[5]; ❷

primes[0] = 2; ❸
primes[1] = 3;
primes[2] = 5;
primes[3] = 7;
primes[4] = 11;

143. Assignment to final variable?

for (int i = 0; i < 5; i++) {
  System.out.println("At index " + i + ": value == " + primes[i]);
}

Result:

At index 0: value == 2
At index 1: value == 3
At index 2: value == 5
At index 3: value == 7
At index 4: value == 11

Combining array allocation and value assignment:

final int[]
  primes = {2, 3, 5, 7, 11};

final int[] primes = new int[5];
primes[0] = 2;
primes[1] = 3;
primes[2] = 5;
primes[3] = 7;
primes[4] = 11;

Combining array allocation and value assignment:

public class Rectangle {
    private int width, height;
    private boolean hasSolidBorder;
    public Rectangle(int width, int height,
                   boolean hasSolidBorder) {
        this.width = width;
        this.height = height;
        this.hasSolidBorder = hasSolidBorder;
    }
}

final Rectangle[] rectList = new Rectangle[] {
  new Rectangle(2, 5, true),
  new Rectangle(4, 1, false)
};

144. Converting string arrays to HTML.
145. Route navigation
146. Examinations and mark frequencies
147. Pangram checker

...println("        String: " + "".getClass().getTypeName());
...println("         int[]: " + new int[]{}.getClass().getTypeName());
...println("      double[]: " + new double[]{}.getClass().getTypeName());
...println("     boolean[]: " + new boolean[]{}.getClass().getTypeName());
...println("StringBuffer[]: " + new StringBuffer[]{}.getClass().getTypeName());

        String: java.lang.String
         int[]: int[]
      double[]: double[]
     boolean[]: boolean[]
      String[]: java.lang.String[]
StringBuffer[]: java.lang.StringBuffer[]

public static void main(String[] args) {
  final int [] lectures = new int[3]; // Three lectures
  fill(lectures, 25); // Default lecture having 25 participants
  System.out.println("Second lecture has got " + lectures[1] +
          " participants");
}
/**
  * Initialize array with default value.
  *
  * @param values Array to be initialized.
  * @param common New value for all array elements.
  */
static void fill(final int[] values, final int common) {
  for (int i = 0; i < values.length; i++) {
    values[i] = common;
  }
}

Second lecture has got 25 participants

// Value type
final boolean values[] = new boolean[]{true, true, false, true};

// Reference type
final String shapes[] = new String[]{"Triangle", "Circle"};

Same result:

final boolean values[] = {true, true, false, true};

final String shapes[] = {"Triangle", "Circle"};

148. Reconsidering System.out.format().

• Arrays
  • ➟ java.util.Arrays helpers

    Sorting and searching arrays.

    Fill in values.

    Compare array contents.

final String[] names = {"Eve", "Aaron", "Paul", "Mandy"};

System.out.println("     toString: " + Arrays.toString(names));

Arrays.sort(names);

System.out.println("sort|toString: " + Arrays.toString(names));

Result:

     toString: [Eve, Aaron, Paul, Mandy]
sort|toString: [Aaron, Eve, Mandy, Paul]

final String[] names = {"Aaron", "Eve", "Mandy",  "Paul"};

// Precondition: Array must be ordered!
...println("sort|find(Mand): " + Arrays.binarySearch(names, "Mand"));
...println("sort|find(Mandy): " + Arrays.binarySearch(names, "Mandy"));
...println("sort|find(Mandyer): " + Arrays.binarySearch(names, "Mandyer"));

Result:

sort|find(Mand): -3
sort|find(Mandy): 2
sort|find(Mandyer): -4

149. Understanding search results

final String[] names = {"Eve", "Aaron", "Paul", "Mandy"};

final String[] lastTwoNames = Arrays.copyOfRange(names, 2, 6);

System.out.println("toString: " + Arrays.toString(lastTwoNames));

Result:

toString: [Paul, Mandy, null, null]

final String[]
  l1 = {new String("Eve"), new String("Aaron"), 
        new String("Paul"), new String("Mandy")},

  l2 = {new String("Eve"), new String("Aaron"), 
        new String("Paul"), new String("Mandy")},

  l3 = {new String("Eve"), new String("Aaron"), 
        new String("Paul"), new String("Mobile")};

System.out.println("l1.equals(l2):" + Arrays.equals(l1, l2));
System.out.println("l1.equals(l3):" + Arrays.equals(l1, l3));

Result:

l1.equals(l2):true
l1.equals(l3):false

• Arrays
  • ➟ Extending arrays

    Dealing with fixed size.

final String[] member = {"Eve", "John", "Peter", "Jill"};

final String newCourseMember = "Ernest";

member.length = 5; // Error: Size unchangeable

member[4] =  newCourseMember;

public static void main(String[] args) {
 ❶ String[] member = {"Eve", "John", "Peter", "Jill"};
  final String newMember = "Ernest";
  member ❷= append(member, newMember);
}
static String[] append (final String[] values, final String newValue) {
  final String[] copy = ❸ new String[values.length + 1];
  for (int i = 0; i < values.length; i++) { ❹
    copy[i] = values[i]; ❺
  }
  copy[copy.length - 1] = newValue; ❻
  return copy;
}

final String[] member = {"Eve", "John", "Peter", "Jill"};
System.out.println("Original array: " + Arrays.toString(member));
final String newMember = "Ernest";
member = append(member, newMember);
System.out.println("Extended array: " + Arrays.toString(member));

Original array: [Eve, John, Peter, Jill]
Extended array: [Eve, John, Peter, Jill, Ernest]

public static void main(String[] args) {
    final int [] start = {1,7,-4},
    added = append(start, 77);
    System.out.println("added: " + Arrays.toString(added));
  }
static public int[] append(final int[] values, final int newValue) {
  final int[] result = Arrays.copyOf(values, values.length + 1);
  result[values.length] = newValue;
  return result;}

Result:

added: [1, 7, -4, 77]

150. Implementing append directly
151. Purge duplicates
152. A container of fixed capacity holding integer values
153. Allow for variable capacity holding integer values

• Arrays
  • ➟ Understanding static public int main(String[] args)

    main(...) and its array argument.

    Implementing parameter passing.

package myapp;
public class Cmd {
  public static void main(String[] args) {
    for (int i = 0; i < args.length; i++) {
      System.out.println("Parameter " + (i + 1) + ": " + args[i]);
    }
  }
}

java myapp.Cmd 21 334 -13
Parameter 1: 21
Parameter 2: 334
Parameter 3: -13

<artifactId>maven-shade-plugin</artifactId>
...
<transformer ...>
  <manifestEntries>
    <Main-Class>myapp.Cmd</Main-Class>
  </manifestEntries>...

unzip ww-1.0-SNAPSHOT.jar
cat  tmp/META-INF/MANIFEST.MF
...
Created-By: Apache Maven 3.5.0
Build-Jdk: 1.8.0_151
Main-Class: myapp.Cmd

mvn package ...
java -jar target/ww-1.0-SNAPSHOT.jar 21 334 -13
Parameter 1: 21
Parameter 2: 334
Parameter 3: -13

154. Reading console input
155. Prettifying output representation

• Arrays
  • ➟ Multi-dimensional arrays

    Multiple dimensions by nesting of arrays.

final int[][] matrix = new int[2][3];

for (int row = 0; row < 2; row++) {
  for (int col = 0; col < 3; col++) {
    matrix[row][col] = col + row;
  }
}
for (int row = 0; row < 2; row++) {
  System.out.println(Arrays.toString(matrix[row]));
}

final int[][] matrix = new int[2][]; // Array containing two int arrays
matrix[0] = new int[3];              // first int array
matrix[1] = new int[3];              // second int array

156. 2-dimensional arrays and .length

final int[][] matrix = new int[][] {
  {0, 1, 2},
  {1, 2, 3}
};

157. External array and string exercises
158. Tic-tac-toe using a two-dimensional array
159. Changing the game's internal representation
160. Tic-tac-toe, Computer vs. human
161. Adding support to retrieve statistical data.
162. Testing an implementation
163. Improving prime number calculation performance
164. Calculating the median
165. A simple character based plotting application