Array Examples & ExceptionsS2C Home « Array Examples & Exceptions

In the last lesson we looked at array manipulation using the Array object, in this lesson we continue our investigation of arrays by showing their usage through code examples and some of the exceptions that can occur when using them.

One Dimensional Array Examples Top

Lets look at some code to illustrate the use of one dimensional arrays:


package info.java8;
/*
  One dimensional array examples 
*/ 
public class OneDimensionArrays {

    public static void main (String[] args) {
  int intArray1[];           // Array declaration
  intArray1 = new int[4];    // Array allocation
  System.out.println("Value of position 4 (index 3) : " + intArray1[3]);
  intArray1[3] = 672;        // Array initialization  
  System.out.println("Value of position 4 (index 3) : " + intArray1[3]);

  String[] strArray1;;       // Array declaration
  strArray1 = new String[3]; // Array allocation
  System.out.println("Value of position 3 (index 2) : " + strArray1[2]);
  strArray1[2] = "fred";     // Array initialization   
  System.out.println("Value of position 3 (index 2) : " + strArray1[2]);

  String strArray2[] = {"one", "aa", "c", "rt", "je"};     // Single statement array creation   
  System.out.println("Value of position 5 (index 4) : " + strArray2[4]);
    }
}

Running the OneDimensionArrays class produces the following output:

run one dimensional arrays
Screenshot 1. Running the OneDimensionArrays class.

You should see 5 lines of output as in the screenshot above. This is is our first look at the new operator which tells the compiler to construct a new instance of the object in question. We use the zero-based index number of the array object to access elements within the array. We are printing an element of the array after the allocation step to show default initialization and the same element after we have initialized it. The last line of output displays an element after a single statement array creation step.

Two Dimensional Array Examples Top

Lets look at some code to illustrate the use of two dimensional arrays:


package info.java8;
/*
  Two dimensional array examples 
*/ 
public class TwoDimensionArrays {

    public static void main (String[] args) {
  int intArray1[][];             // Array declaration
  intArray1 = new int[3][4];     // Array allocation
  for (int i=0; i<intArray1.length; i++) {  // Array initialization using a for loop 
          for (int j=0; j<intArray1[i].length; j++) {
               intArray1[i][j] = i + j;
               System.out.println("Array position: " + i + ":" + j + " = " + intArray1[i][j]);
          }
  }
   // Single statement array creation
  int[][] intArray2 = new int[][]{ {5, 33}, {0}, {5, 4, 71} }; // Irregular array
  for (int i=0; i<intArray2.length; i++) { 
          for (int j=0; j<intArray2[i].length; j++) {
              System.out.println("Array2 position: " + i + ":" + j + " = " + intArray2[i][j]);
          }
  }
    }
}

Running the TwoDimensionArrays class produces the following output:

run two dimensional arrays
Screenshot 2. Running the TwoDimensionArrays class.

The above screenshot shows the output of a couple of two-dimensional arrays. The first regular array is created using multiple statements and initialized using two for loops; we print the elements as we initialize them. The second irregular array is created using a single statement; we then use a couple of for loops to cycle through the array printing out the element values. We are using the anArray.length code to form the loop iteration. Each array has a length variable associated with it and because arrays are zero-index based this is a perfect way of looping through all the elements of an array.

java.lang Array Exceptions Top

As mentioned in the Getting Started lesson all our programs implicitly import the java.lang Package. Within this package are classes of exceptions we talk about in great detail in the Exceptions section of the site. For now we are purely interested in those exceptions that can be thrown by our arrays.

NegativeArrayCreation Exception Top

Following is example code and a screenshot of the runtime error when trying to access an array with a negative array allocation:


package info.java8;
/*
  Negative array creation
*/ 
public class NegativeArrayCreation {

    public static void main (String[] args) {
        int negativeArray[]; // Array declaration
        negativeArray = new int[-2]; // Negative array allocation
        negativeArray[0] = 672; // Array initialization  
    }
}

Running the NegativeArrayCreation class produces the following output:

run negative array
Screenshot 3. Running the NegativeArrayCreation class.

As you can see when we try to run the NegativeArrayCreation class we get a NegativeArraySizeException exception.

ArrayOutOfBoundsException Exception Top

Following is example code and a screenshot of the runtime error when trying to access an array element outside the allocation for that array:


package info.java8;
/*
  Out of bounds example
*/ 
public class OutOfBoundsArray {

    public static void main (String[] args) {
        String strArray[] = {"one", "aa"}; // Single statement array creation   
        System.out.println("Position 3 (index 2) : " + strArray[2]); // Access outside allocation
    }
}

Running the OutOfBoundsArray class produces the following output:

run out of bounds array
Screenshot 4. Running the OutOfBoundsArray class.

As you can see when we try to run the OutOfBoundsArray class we get an ArrayOutOfBoundsException exception as we are trying to access an index outside the bounds of the array.

ArrayStoreException Exception Top

Following is example code and a screenshot of the runtime error when trying to store an invalid type into an array:


package info.java8;
/*
  Invalid type example
*/ 
public class StoreArrayCreation {

    public static void main (String[] args) {
        Number[] anArray = new Float[1]; // Array declaration
        anArray[0] = new Integer(1); // Invalid type
    }
}

Running the StoreArrayCreation class produces the following output:

run store array exception
Screenshot 5. Running the StoreArrayCreation class.

As you can see when we try to run the StoreArrayCreation class we get an ArrayStoreException exception as an Integer object is an invalid type for this Float object array.

Related Quiz

Objects & Classes Quiz 2 - Array Examples & Exceptions

Lesson 2 Complete

In this lesson we looked at some examples of using Array objects and some exceptions that can happen when using them.

What's Next?

In the next lesson we look at class structure and syntax within our Java programs.