02. Java Basics

• The only possible values are true or false (default value for a class-scope boolean variable is false)

• println() will display true or false (not 1 or 0, as in C/C++)

• No casting is allowed from boolean to int or vice-versa (unlike C/C++), so you cannot assign an int expression to a boolean variable nor a boolean expression to an int variable

BITWISE Operators

• Bitwise operators (like the C/C++ bitwise operators) manipulate data bit by bit (i.e., the corresponding bits of the operands are operated on) and may be applied only to integral operands: byte, short, int or long.

&   bitwise AND (1 if both corresponding bits are 1)

|    bitwise OR ( 1 if at least one corresponding bit is 1)

^   bitwise exclusive OR (1 only if one corresponding bit is 1)

<< left shift (shifts left operand the # of bits specified by right operand

>> right shift with sign extension

>>>  right shift with zero extension

~   one's complement (unary: changes 1's to 0's and 0's to 1's)

/*

short num1, num2, mask;        // assume num1 has been assigned a number, doesn't matter what

Exercise 2.1 Write Java statements using the above variables to assign bits 4, 5, 6, and 7 (counting the left-most as bit 0) to num2, but in the least significant bits of num2 (bits 12, 13, 14 and 15). Hints: shift num1 so bit 4 is in position 12, then use a mask of 0x000F and the correct bitwise operator to get the result specified.

*/

public class Exercise_2_1

{

    public static void main(String[] args)

    {

        short num1, num2, mask;                       // 0123 4567 8901 2345

        num1 = 0x0573;                                // num1 = 0000 0101 0111 0011

        mask = 0x000F;                                // mask = 0000 0000 0000 1111

        num2 = (short) (mask & (num1 >>> 8));         // num2 = 0000 0000 0000 0101

        System.out.println("num1: " + Integer.toHexString(num1) + "\nmask: " + Integer.toHexString(mask) + "\nnum2: " + Integer.toHexString(num2));

    }

}

Arithmetic operators:

+       Addition

-        Subtraction

*        Multiplication

/        Division (integral result if both operands are integral)

%      Modulus (remainder of integer division)

 - (unary) Arithmetic negation         + (unary)

Cast Operator:

• To change the type of an expression, you may give the type in parentheses in front of the expression: (type) expression

• Examples:  d1 =(double) i1/i2;

                     i2 = (int)(d1+d2);

Shorthand Assignment Operators:

• Any operation with an assignment such as: var = var operator operand

• can be written as: var operator= operand

boolean Operators:

• NOTE: ALL boolean operators result in true or false, unlike C (NOT 1 or 0).  Also, ALL boolean variables must be assigned a boolean expression (results in true or false, so unlike C, not any non-zero or zero value)!

Relational Operators:

• evaluate to true or false

          OPERATORS:

                   <       less than

                   >       greater than

                   <=    less than or equal to

                   >=    greater than or equal to

                   ==    is equal to

                   !=      not equal to

Logical Operators:

/*Exercise 2.2 Change the following C/C++ code to legal Java code:

*    int inum1=5, inum2=8;

*    while( inum1-- ){ // OK in C, NOT in Java

*    printf("%d", inum1);

*    } // end while

*/

public class Exercise_2_2

{

    public static void main(String[] args)

    {

        int inum1=5, inum2=8;

        while( inum1-- != 0 )

        {

            System.out.println(inum1);

        } // end while

    }

}

/* Exercise 2.3 Change the following incorrect Java code (won't compile because you're trying to re-declare inum2):

    int inum1=10, inum2;

    for(int i=0, inum2=inum1; i < inum2; ++i, --inum2){

    System.out.println("i = " + i);

    } // end for

    System.out.println("The last value of inum2 = "+inum2);

 */

public class Exercise_2_3

{

    public static void main(String[] args)

    {

        int inum1 = 10, inum2;

        inum2 = inum1;

        for(int i=0; i < inum2; ++i, --inum2){

        System.out.println("i = " + i);

        } // end for

        System.out.println("The last value of inum2 = "+inum2);

    }

}

/* Exercise 2.4 Write Java code to print (lined up in columns) numbers from 2 to 20, their squares and their cubes, using a for loop (declare variables for the number as an int, and the square and cube as doubles). Use System.out.printf and right-justify the numbers.

*/

public class Exercise_2_4

{

    public static void main(String[] args)

    {

        int i_num = 2;

        double d_square, d_cube;

        for(int i=2; i <= 20; i++, i_num++)

        {

            d_square = i_num * i_num;

            d_cube = i_num * i_num * i_num;

            System.out.printf("%d %8.2f %8.2f \n", i_num, d_square, d_cube);

        }

    }

}