Java Arrays

Java Arrays

• 1.
  Java Arrays JussiPohjolainen Tampere University of Applied Sciences
• 2.
  Types Java hastwo kind of types Primitive Types int, byte, short, long, double, float, boolean, char Class Types Everything else, for example String, Scanner, Arrays , Vector, JButton, JCheckBox
• 3.
  Problem? Implement anapplication that will calculate 100 students exam average. Variables needed? int studentA; int studentB; int studentC; int studentD; ...
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  Several Variables atOnce? Array comes to the rescue! Just a list of variables Declare the array int [] array; Initialize the array and set it's size array = new array[3]; Store values into array array[0] = 2; array[1] = 3; array[2] = 7;
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  Array int []myarray = new int[3]; myarray[0] = 1; myarray[1] = 12; myarray[2] = 88; System.out.println(myarray[0]); System.out.println(myarray[1]); System.out.println(myarray[2]);
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  myarray index length= 3 0 1 2 1 12 88
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  Indexes The valuescan be retrieved from the array using index. The first value is found from index 0 and the last from length – 1 int [] myarray = new int[LENGTH]; myarray[0] = 1; // first one myarray[LENGTH-1] = 22; // last one
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  Initializing the Arraywith {} int [] myarray = new int[3]; myarray[0] = 2; myarray[1] = 8; myarray[2] = 12; <=> int [] myarray = {2,8,12};
• 9.
  Common Problems int[] myarray1 = {2,8,12}; int [] myarray2 = new int[3]; // Output? System.out.println(myarray1[3]); // Output? System.out.println(myarray2[0])); // Output? System.out.println(myarray1);
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  Example 1 int[] myarray = {2,8,12}; int i = 0; while(i < 3) { System.out.println(myarray[i]); i++; }
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  Example 2 int[] myarray = {2,8,12}; int i = 0; while(i < myarray.length ) { System.out.println(myarray[i]); i++; }
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  Example 3 int[] myarray = {2,8,12}; for(int i = 0; i < myarray.length; i++ ) { System.out.println(myarray[i]); }
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  Example 3 int[] myarray = new int[3]; for(int i = 0; i < myarray.length ; i++ ) { myarray[i] = myscanner.nextInt(); } for(int i = myarray.length-1; i >= 0 ; i++ ) { System.out.println(myarray[i]); }
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  COMMAND LINE ARGUMENTS
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  Command Line Argument?public class CommandLine { public static void main( String [] args ) { } } Declaration of an array!
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  Command Line Argument?> java CommandLine Hello World Hello World public class CommandLine { public static void main( String [] args ) { System.out.println(args[0]); System.out.println(args[1]); } }
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  About Command LineArgument Command line argument is user input from the command line Argument array is initialized automatically for you (size and content)
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  What can gowrong? > java CommandLine 10 5 10 / 5 = 2 public class CommandLine { public static void main( String [] args ) { int a = Integer.parseInt(args[0]); int b = Integer.parseInt(args[1]); int result = a / b; System.out.print(&quot;&quot; + a + &quot; / &quot; + b + &quot; = &quot;); System.out.println(result); } }