- Recall that:
- Internally
(= inside a computer program),
(signed) integer values
are represented
using the
2's complement code:
Value Internal representation (in 32 bits) ------------ ---------------------------------------- ... ... neg three 11111111111111111111111111111101 neg two 11111111111111111111111111111110 neg one 11111111111111111111111111111111 zero 00000000000000000000000000000000 one 00000000000000000000000000000001 two 00000000000000000000000000000010 three 00000000000000000000000000000011 ... ... twelve 00000000000000000000000000001100 ... ...The 2's complement representation is very efficient to perform arithmetic calculations
(See: click here )
- Internally
(= inside a computer program),
(signed) integer values
are represented
using the
2's complement code:
- Numbers are
entered into the
computer input by
typing the
text:
For example: 12 123 ...Problem:
- When you type in the text
12
the computer will receive these ASCII codes:
00110001 00110010 which represents the characters: 1 2The computer will not receive the 2;s complement code 00001100 for the value twelve !!!
- See it for yourself:
- Enter the text "true" or "false":
- See the corresponding binary ASCII codes for the string:
- Enter the text "true" or "false":
- When you type in the text
- In other words:
- Human users will
enter the
number 12 as a
string "12"
(i.e.: as ASCII codes
representing the characters
1 and
2)
- But internally (= inside a Java program, the boolean values are represented by the binary numbers 00000001 and 00000000
Therefore: we need to convert the input (ASCII) representation to the internal int (2's complement) representation
- Human users will
enter the
number 12 as a
string "12"
(i.e.: as ASCII codes
representing the characters
1 and
2)
- The Java class Integer
has provide the
conversion method
parseInt( ) to
Java programmers to do the
conversion.
In CS170/CS171, you have learned to use this method.
Example:
int i; String s = "123"; i = Integer.parseInt(s); // Convert string s to integer representationIn CS255, we will reveal the secret inside the parseInt( ) method so you will understand the computer operation better.
Unlike the Boolean example, the conversion from ASCII representation of numbers to 2's complement representation of numbers is more complex and will take more than 1 webpage to explain....