Classes Basics

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Introduction

This chapter examines the operators used in the Java language. We have already used some operators such as "=" and "+" in previous sections.

Arithmetic

The "%" modulus operatos takes 2 argument and returns the remainder.

Example:
  10 % 3  produces 1
  10 % 5  produces 0

We also have the addition assignment operator "+=" . This adds the number on the right to the value of the variable on the left and assigns it the sum valu to the value on the left.

  int x1 = 5 ;

  x1 += 2 ; //x1 is now 7
  //Same as
  x1 = x1 + 2 ;

  x1 -= 3 ;
  //Same as
  x1 = x1 - 3 ;

  Also
  x1 *= 2 ;
  //Same as
  x1 = x1 * 2 ;

  x1 /= 2 ;
  //Same as
  x1 = x1 / 2 ;

Auto increment

This operator can increment or decrement a value. We have 2 types "postfix" and "prefix". The difference is the point of time that the variable is updated at.

 int x1 = 10 ;
 //Prints 11
 System.out.println( ++x1 ) ;
 //Prints 11
 System.out.println( x1 ) ;

 //Prints 11
 //Change is not done at the below line.
 System.out.println( x1++ ) ;
 //Change is made at this point
 //Prints 12
 System.out.println( x1 ) ;

File: Increment.java

public class Increment
{
    public static void main( String args[] )
    {
        int x1 = 5 ;
        int y1 = 5 ;
        int z1 ;

        //x1 is still 5 and y1 becomes 6 so z1 is 11
         z1 = x1++ +  ++y1 ;
         //z1 11
         //Now x1 is 6  y1 is 6
        //z1 prints 11
        System.out.println(  "z1 = " + z1 ) ;
        //x1 is 6 and y1 is 6
         z1 = x1++ +  y1++ ;
         //z1 is 12
          // x1 is now 7 and y1 is 7
         System.out.println( "z1 = " + z1 ) ;

          z1 = x1 +  y1 ;
          //z1 is now 14
          System.out.println( "z1 = " + z1 );
          //z1 is still 14 and will only change it's value
          // after the conditional expression
          if ( z1++ == 14 )
             z1++ ;
         //After the conditional expression z1 is 15 and now we have another "++" so z1 is 16
          ++z1 ;  //Now z1 is 17
         System.out.println( "z1 = " + z1 ) ;
             //17


      }


} //class
C:\WebSite\Learn\2\Java\intro>java Increment
z1 = 11
z1 = 12
z1 = 14
z1 = 17

Similar to the increment operators we have the decrement operators.

File: Decrement.java

public class Decrement
{
    public static void main( String args[] )
    {
            int x1 = 12 ;
            int y1 = 12 ;
            int z1 ;
            z1 = x1-- +  --y1 ;
            System.out.println( "z1 = " + z1  );
            z1 = x1-- +  y1-- ;
            System.out.println( "z1 = " + z1  );

            z1 = x1 +  y1 ;
            System.out.println( "z1 = " + z1  );
            if ( z1-- == 20 )
                z1-- ;
           // After the conditional expression z1 is 19
           // and now we have another "--" so z1 is 18
              --z1 ;
              //Now z1 is 17
            System.out.println( "z1 = " + z1  );


      }


} //class
C:\WebSite\Learn\2\Java\intro>java Decrement
z1 = 23
z1 = 22
z1 = 20
z1 = 17

Comparision

File: Relational.java

public class Relational
{
    public static void main( String args[] )
    {
        int x1 = 5 ;
        int y1 = 5 ;
        Integer n1 = new Integer(47);
        Integer n2 = new Integer(47);
        //We know the below is false because
        //== compares addresses and not the contents
        System.out.println(n1 == n2);
        System.out.println(n1 != n2);
        //Must use equals
        System.out.println( n1.equals(n2) );

        System.out.println( "x1 < y1 :" +
             (x1 < y1) );
        System.out.println( "x1 <= y1 :" +
                (x1 <= y1)  );
        //True if x1 is not equal to y1
        System.out.println( "x1 != y1 :" +
                (x1 != y1)  );

         y1 = 6 ;
        //&& Check if both conditions are true
        System.out.println( "((x1 < y1) && (y1 == 6 )) :" +
             ((x1 < y1) && (y1 == 6 )) );

        //|| Check if one condition is true
        System.out.println( "((x1 < y1) || (y1 == 6 )) :" +
             ((x1 < y1) || (y1 == 6 )) );

        //Short circuiting
        //If the first condition is false then the result will be
        //false so no need to evaluate (y1 == 6)
        System.out.println( "((x1 > y1) && (y1 == 6) ) :" +
             ((x1 > y1) && (y1 == 6 )) );

        //If the first condition is true the second condition
        //is not evaluated.
        System.out.println( "((x1 < y1) || (y1 == 6 )) :" +
             ((x1 < y1) || (y1 == 6 )) );


    }


} //class
C:\WebSite\Learn\2\Java\intro>java Relational
false
true
true
x1 < y1 :false
x1 <= y1 :true
x1 != y1 :false
((x1 < y1) && (y1 == 6 )) :true
((x1 < y1) || (y1 == 6 )) :true
((x1 > y1) && (y1 == 6) ) :false
((x1 < y1) || (y1 == 6 )) :true

Bitwise Operators

File: Binary.java

public class Binary
{
    public static void main( String args[] )
    {
       int i1 = 0x2f; //2f is a hexadecimal
       System.out.println( "i1: " + i1 ) ;

        // 6.022 * 10 power 23
       double largeValue = 6.022e23;
       System.out.println( "largeValue: " + largeValue ) ;


       int binaryNumber1 = 0b1101;
       int binaryNumber2 = 0b0100;
       //Operator & 2 bits and to 1 if both are 1 else
       //the result is 0
       System.out.println( "binaryNumber1 & binaryNumber2 " +
                (binaryNumber1 & binaryNumber2)  ) ;
       System.out.println( Integer.toBinaryString(
           binaryNumber1 & binaryNumber2)  ) ;

       //Operator | on 2 bits and is 1 if any bit is 1
       System.out.println( "binaryNumber1 | binaryNumber2: " +
       (binaryNumber1 | binaryNumber2) ) ;
       System.out.println( Integer.toBinaryString(
           binaryNumber1 | binaryNumber2)  ) ;

       byte binaryNumber3 = (byte)0b00000101;
       byte binaryNumber4 = (byte)0b11111111;
       System.out.println( binaryNumber3 ) ;
       System.out.println( binaryNumber4 ) ;
       binaryNumber3 = (byte)( binaryNumber3 << 1 ) ;
        System.out.println( binaryNumber3 ) ;

       //Since the no is negative 1's are inserted to the left
       binaryNumber4 = (byte)( binaryNumber4 >> 1 ) ;
       System.out.println( binaryNumber4 ) ;

       // binaryNumber4 is still -1 at this point
       // 0 is inserted on the left hand side
       System.out.println( "---" ) ;
       System.out.println( binaryNumber4  ) ;
       // binaryNumber4 is -1 so expecting 0's inserted on the
       //left hand side
       //Works properly
       System.out.println( binaryNumber4 >>> 1  ) ;
       binaryNumber4 = (byte)( binaryNumber4 >>> 1 ) ;
       System.out.println( binaryNumber4 ) ;

       System.out.println( binaryNumber4 >>> 1 ) ;
        //Only retains the right most 8 bits which
        //are all ones
        System.out.println( (byte)binaryNumber4 ) ;

        System.out.println( "---" ) ;
        System.out.println( binaryNumber4 >>> 1  ) ;
               binaryNumber4 = (byte)( (byte)binaryNumber4 >>> 1 ) ;

    }


} //class
C:\WebSite\Learn\2\Java\intro>java Binary
i1: 47
largeValue: 6.022E23
binaryNumber1 & binaryNumber2 4
100
binaryNumber1 | binaryNumber2: 13
1101
5
-1
10
-1
---
-1
2147483647
-1
2147483647
-1
---
2147483647

String

File: StringOp.java

public class StringOp
{
    public static void main( String args[] )
    {
        int x1 = 1 , x2 = 2 , x3 = 3 ;
        String str1 = "Int Variables" ;
        String fName = "Archie " ;
        String lName = "Moore" ;
        //+ is the string concatenation operator
        //println converts the variables to integers
        System.out.println( str1 + x1 + x2 + x3 ) ;
        System.out.println( str1 + (x1 + x2 + x3) ) ;

        String str2 ;
        //StringOp.java:17: error: incompatible types: int cannot be converted to String
        // No automatic conversion
        // str2 = x1 ;
        str2 = Integer.toString( x1 ) ;

        //concatenate 2 strings using +
        String fullName = fName + lName ;
        System.out.println( fullName ) ;

        //Can use the += operator
        fullName += " Boxer" ;
        System.out.println( fullName ) ;



    }


} //class

Rounding

public class Rounding
{
    public static void main( String args[] )
    {
        int x1 = 1 , x2 = 2 , x3 = 3 ;
        float f1 = 0.7f ;
        float f2 = 0.3f ;

        //By default .7 is a double not a float
          double d1 = 0.7 ;
          //int casts truncates the number
        System.out.println(  (int)f1 )  ;
        System.out.println(  (int)f2 )  ;
        System.out.println(  (int)d1 )  ;

        System.out.println(  Math.round(f1) )  ;
        System.out.println(  Math.round(f2) )  ;
        System.out.println(  Math.round(d1) )  ;

    }


} //class