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					                      NLP-AI
                 Java Lecture No. 4


          Operators & Decision Constructs
                      Satish Dethe
                 <satishd@cse.iitb.ac.in>
03 August 2004
                           Contents

• Increment Operator
• Decrement Operator
• Boolean Data Type
• Relational Operators
• Equality Operators
• Conditional Operators
• Selectional Constructs



03 August 2004
                         nlp-ai@cse.iitb
                       Increment Operators


• i + + first use the value of i and then increment it by 1.
      „i + +‟ equivalent to „i = (i)+1‟. // postfix increment
• + + i first increment the value of i by 1 and then use it.
      „+ + i‟ equivalent to „i = (i+1)‟. // prefix increment
      int i=2;
•System.out.print(“ i = ”+ i++);//print 2, then i becomes 3
•System.out.print(“ i = ”+ ++i);//add 1 to i, then print 4
•Refer to incre.java

03 August 2004
                           nlp-ai@cse.iitb
                      Decrement Operators



• i - - first use the i ‟s value and then decrement it by one
        i - - equivalent to (i)-1. // postfix decrement
• - - i first decrement i ‟s value by one and then use it.
        - - i equivalent to (i-1). // prefix decrement

int i=5;
System.out.print(“i = ” + i--);//print 5, then i becomes 4
System.out.print(“i = ” + --i);//subtract 1 from i, then print 3
Refer to decre.java



03 August 2004
                          nlp-ai@cse.iitb
                         Boolean Data Type

This data type can store only two values; true and false.
Declaring a boolean variable is the same as declaring any other
primitive data type like int, float, char.
boolean          response = false; //Valid
boolean          answer = true;      //Valid
boolean          answer = 9943;      //Invalid,
boolean          response = “false”; // Invalid,

This is return type for relational & conditional operators.

Refer to bool_op.java


03 August 2004
                               nlp-ai@cse.iitb
                       Relational Operators

a < b        a less than b. (true/false)
a <= b a less than or equal b. (true/false)
a > b a greater than b. (true/false)
a >= b a greater than or equal to b. (true/false)
    These operations always return a boolean value.
System.out.println(“23 is less than 65 ” +23<65); // true
System.out.println(“5 is greater than or equal to 25.00?” +
5>=25.00); // false
Refer to relate.java

03 August 2004
                             nlp-ai@cse.iitb
                        Equality Operators

a==b             a equal to b. (true/false)
a!=b             a not equal to b. (true/false)


boolean equal = 12 = = 150; // false

 boolean again_equal = „r‟= = „r‟); // true
boolean not_equal = 53!=90); // true


Refer: equa.java


03 August 2004
                              nlp-ai@cse.iitb
                    Conditional Operators

•A conditional operator is used to handle only two boolean
expressions.
  Boolean expression always returns ‘true’ or ‘false’.
•Conditional AND „&&‟
 Return value is „true‟ if both, x and y are true, else it is „false‟.
System.out.println(“x&&y ” + x&&y); // Refer cond_and.java

•Conditional OR „||‟
return value is true if any one of x or y, is true else it is false.
System.out.println(“x||y ” + x||y); // Refer cond_or.java

  03 August 2004
                             nlp-ai@cse.iitb
                              The ‘ if ’ construct

It is used to select a certain set of instructions. It is used to decide
whether this set is to be carried out, based on the condition in the
parenthesis. Its syntax is:
if (<boolean expression>){
//body starts
         <statement(s)>
//body ends
}
The <boolean expression> is evaluated first. If its value is true, then
the statement(s) are executed. And then the rest of the program. Refer
if_cond.java, if_cond1.java
    03 August 2004
                                 nlp-ai@cse.iitb
                   The „if else’ construct

It is used to provide an alternative when the expression in if is
    false. Its syntax is:
if(<boolean expression>){
          <statement(s)>
}
else{
          <statement(s)>
}
The if construct is the same. But when the expression inside if
    is false then else part is executed.
Refer ifelse_cond.java

 03 August 2004           nlp-ai@cse.iitb
                        Assignments

int a_number=1; // (range: 1 to 5 including both)
Print the value of a_number in word. For example, it should print
      “Four” if a_number contains 4.

1.    Use equality „= =‟ operator.
2.    Do not use equality „= =‟ operator.




 03 August 2004           nlp-ai@cse.iitb
                     End




                 Thank You!




03 August 2004
                 nlp-ai@cse.iitb

				
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Description: java and its various features
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