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Primitive data types

1. Uses of identifiers in Java | 2. Primitive data types in Java

• Are part of the language (built-in)

• Represent different kinds and sizes of data

• Are always the same regardless of the platform

What about strings?

• There is no primitive data type in Java to represent strings (such as "Java is fun")

• Several packaged classes provide for string manipulation and will be covered later

What is Unicode?

• An international (ISO) standard. For detailed information, go to http://www.unicode.org/

• Provides a unique bit pattern to represent every character or symbol in all the world's character sets

• Each character has an equivalent, positive integer value corresponding to the bit pattern

Integer data format

Uses two's-complement notation. To determine the bit pattern of an integer value:

1. If the number is greater than or equal to zero: convert it to binary

2. If the number is negative: take its absolute value, subtract one, convert the result to binary, and reverse all the bits

The left-most (high-order) bit is the sign bit with 0 indicating positive and 1 indicating negative.

Here are some examples using a 16 bit (short) data format:

For simplicity, hexadecimal (base 16) notation is used to represent binary numbers. Each hexadecimal digit represents four binary digits as follows:

Floating-point (decimal) types

• Conform to the IEEE 754 specification for representing real numbers in a binary format. For the certification exam, you will not need to know the internal representation or the range of maximum and minimum values.

• double allows up for twice as many significant digits as float and should be used when extremely large numbers or greater precision are required

More information

Java ranch has two great tutorials relating to topics covered in this lesson. Be sure to read the following "campfire stories":

• Cup Size -- a story about variables

• Cat and Mouse Games with Bits

Review questions

1. Which of the following are valid Java identifiers? (choose three)

1. _$amount_due_2002

2. 2002_sales

3. class

4. String

5. FINANCE_CHARGE

2. Which primitive data type may be used to store the integer value -473 ? (choose three)

1. char

2. byte

3. short

4. int

5. long

3. Which of the following hexadecimal values might represent the contents of a negative, int variable? (choose two)

1. 1AF21110

2. C8253B7C

3. F63A

4. FFFFFFFFFFFFFFFF

5. 90001C58

4. In hexadecimal notation, what is the value of -100 as a byte?

1. FF9C

2. 9C

3. FF9B

4. 9B

5. a byte is too small an area to hold the value

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