A Touch of Java

Part 1: assignment statements

PGSS Computer Science Core Slides

Java programs consist of many statements:

After covering each, we'll put them together in functions.

Now, we examine assignment statements.


Java programs abstract the concept of memory addresses with variables. A variable reserves a segment of memory for a given type of data.

We'll use three types, corresponding to the ones we saw earlier.

	 char     character
	 int      integer
	 double   floating-point number

Variable declarations

Before using variables, we must first declare them to reserve memory and to assign type.

  int variable_name0;

The int gives the type of variable. variable_name0 is the name of the variable (consisting of letters, digits, and underscores, but beginning with a letter). The semicolon ends the statement.

Other examples:

  char character;
  int k;
  double root_n;

Assignment statements

To give a value to a variable, we use an assignment statement.

  k = 2;

Here k is the variable to be changed. The value to give it is 2. And we see yet another statement-terminating semicolon.

The right-hand side can be any expression. Some expressions:

   4        9 + k         30 / 4          12 - 3 * 4
   k        3 * k        30.0 / 4        (12 - 3) * 4
  -k        6 - 9         20 % 4

So we can also write:

  k = 9 * k * k + 6;


We reserve long blocks of memory with arrays. To declare an array of 30 characters, we write

  char[] arr = new char[30];
Here the type of array element (char) occurs twice. We have named the array array, and the number appearing in brackets (30) is the array length.

We use an index in brackets to specify array elements in assignments.

  arr[0] = 'S';
  arr[k / 2] = '0';

Note: Arrays are indexed from 0. So arr[30] doesn't exist.

Multi-dimensional arrays

Arrays of arrays, too, are OK, as are arrays of arrays of arrays (and deeper). An array of arrays is a two-dimensional array.

  double[][] m = new double[4][5];

Access is as before.

  m[k - 39][4] = k / 3 / 2;
  m[0][0] = m[3][4] / k;