Java Arrays
Download as PPT, PDF•7 likes•8,049 views
- Arrays allow storing multiple values in a single variable. They are useful for problems that require working with several variables at once, like calculating exam averages for 100 students. - Arrays are initialized with a size and values can be stored and retrieved using indexes. Common issues include accessing indexes outside the array bounds or failing to initialize arrays properly. - Command line arguments provide a way to pass user input to a program via the command line when it is launched. The arguments are stored in a String array that is initialized for the program.
![Several Variables at Once? 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;](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-4-320.jpg)
![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]);](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-5-320.jpg)
![Indexes The values can 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](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-7-320.jpg)
![Initializing the Array with {} int [] myarray = new int[3]; myarray[0] = 2; myarray[1] = 8; myarray[2] = 12; <=> int [] myarray = {2,8,12};](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-8-320.jpg)
![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);](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-9-320.jpg)
![Example 1 int [] myarray = {2,8,12}; int i = 0; while(i < 3) { System.out.println(myarray[i]); i++; }](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-10-320.jpg)
![Example 2 int [] myarray = {2,8,12}; int i = 0; while(i < myarray.length ) { System.out.println(myarray[i]); i++; }](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-11-320.jpg)
![Example 3 int [] myarray = {2,8,12}; for(int i = 0; i < myarray.length; i++ ) { System.out.println(myarray[i]); }](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-12-320.jpg)
![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]); }](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-13-320.jpg)
![Command Line Argument? public class CommandLine { public static void main( String [] args ) { } } Declaration of an array!](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-15-320.jpg)
![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]); } }](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-16-320.jpg)
![What can go wrong? > 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("" + a + " / " + b + " = "); System.out.println(result); } }](https://image.slidesharecdn.com/arrays-091107061255-phpapp01/85/Java-Arrays-18-320.jpg)
Java Arrays
- 1. Java Arrays Jussi Pohjolainen Tampere University of Applied Sciences
- 2. Types Java has two 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 an application that will calculate 100 students exam average. Variables needed? int studentA; int studentB; int studentC; int studentD; ...
- 4. Several Variables at Once? 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;
- 5. 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]);
- 6. myarray index length = 3 0 1 2 1 12 88
- 7. Indexes The values can 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
- 8. Initializing the Array with {} 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);
- 10. Example 1 int [] myarray = {2,8,12}; int i = 0; while(i < 3) { System.out.println(myarray[i]); i++; }
- 11. Example 2 int [] myarray = {2,8,12}; int i = 0; while(i < myarray.length ) { System.out.println(myarray[i]); i++; }
- 12. Example 3 int [] myarray = {2,8,12}; for(int i = 0; i < myarray.length; i++ ) { System.out.println(myarray[i]); }
- 13. 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]); }
- 15. Command Line Argument? public class CommandLine { public static void main( String [] args ) { } } Declaration of an array!
- 16. 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]); } }
- 17. About Command Line Argument Command line argument is user input from the command line Argument array is initialized automatically for you (size and content)
- 18. What can go wrong? > 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("" + a + " / " + b + " = "); System.out.println(result); } }