Arrays

• Array: Sequence of values of the same type

• Construct array: new double[10]    //10 is the number of elements, not index.

• Store in variable of type double[]

double[] value = new double[10];

• Click here for an example.

• When array is created, all values are initialized depending on array type:

  • Numbers: 0

  • Boolean: false

  • Object References: null

• There is another way to initialize an array.

int[] squares = {0. 1, 4, 9, 16};

String[] friends = {"Emily", "Bob", "Cindy"};

• Using the value stored:

System.out.println("The value of this data item is " + value[2]);

• Get array length as value.length (Not a method!) (It is a final instance variable)

• Index values range from 0 to length - 1

• Accessing a nonexistent element results in a bounds error

double[] value = new double[10];
value[10] = 29.95; // ERROR

• Limitation: Arrays have fixed length

What elements does the data array contain after the following statements?

double[] data = new double[10];
for (int i = 0; i < data.length; i++) data[i] = i * i;

Answer: 0, 1, 4, 9, 16, 25, 36, 49, 64, 81, but not 100

What do the following program segments print? Or, if there is an

error, describe the error and specify whether it is detected at

compile-time or at run-time.

1. double[] a = new double[10];
   System.out.println(a[0]);

2. double[] b = new double[10];
   System.out.println(b[10]);

3. double[] c;
   System.out.println(c[0]);

   Answer:

1. 0.

2. a run-time error: array index out of bounds

3. a compile-time error: c is not initialized