2. Java Basics. Java Statements

1. 2. Java Basics

2. Java Statements

2. Comments

• /* . . . */ - multi line comment
• // . . .
- single-line comment
• /** . . . */ - comment for documentation. It
can include some additional tags (e.g.
@version, @author, @param, @return).
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3. How to Use Comments

• Comments should be used to give overviews
of code and provide additional information
that is not readily available in the code itself
• Comments should contain only information
that is relevant to reading and understanding
the program
• Doc comments describe Java classes,
interfaces, constructors, methods, and elds
• Java associates documentation comments
with the rst declaration after the comment
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4. Variables

• Variables declaration: int k;
double x = 2.1;
• Local variable should be initialized before it
will be used.
• Variable scope is a block where it was
declared.
• Sub block can’t contain duplicated variable
declaration.
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5. 1. What will this program output?

public class InitTest {
public static void main (String[] args) {
int a = 5;
int b;
if (a < 0) b = 10;
if (a >= 0) b = 50 ;
System.out.println(b);
}
}
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6. 2. What will this program output?

public class Oblzm {
public static void main (String args[]){
int i = 5;
{
int j = 2;
System.out.println("Result is " + i * j);
}
}
}
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7. 3. What will this program output?

public class Oblzm {
public static void main (String args[]){
int i = 5;
{
int j = 2;
}
System.out.println("Result is “ + i * j);
}
}
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8. 4. What will this program output?

public class Oblzm {
public static void main (String args[]){
int i = 5;
{
int j = 2;
int i = 4;
System.out.println("Result is " + i * j);
}
}
}
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9. Constant Declaration

• final modifier: final int a = 42;
// a = 12; - compile error
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10. If-Then_Else Statement I

if (boolean_expression) {
statements
}
if (boolean_expression) {
statements
} else {
statements
}
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11. If-Then_Else Statement II

if (boolean_expression) {
statements;
} else if (boolean_expression) {
statements;
} else if (boolean_expression) {
statements;
}
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12. If-Then-Else Example

int a = 10;
if (a > 0) {
System.out.println("Positive");
}
else if (a < 0) {
System.out.println("Negative");
}
else {
System.out.println("Zero");
}
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13. Switch Statement

switch(integral-expression) {
case integer-value1 :
statements;
case integer-value2 :
statements;
break;
case integer-value3 :
statements;
break;
default:
statements;
}
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14. Switch Example

char c = ’b’;
switch(c) {
case ’a’:
case ’e’:
case ’i’:
case ’o’:
case ’u’:
print("vowel");
break;
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case ‘y’:
case ‘w’:
print("Sometimes a vowel");
break;
default:
print("consonant");
}
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15. Switch Statement Expressions

• You can use enumerations as switch
expression and case values
• You can use strings as switch expression and
case values (since Java 7 only!)
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16. While and Do-While Statement

while (boolean_expression) {
statements;
}
do {
statements;
} while (boolean_expression);
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17. While Example

double a = 100.;
while (a >= 1) {
System.out.println(a);
a /= 2.;
}
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18. Do-While Example

double a = 0.5;
do {
System.out.println(a);
a /= 2.;
} while (a >= 1);
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19. For Statement

for (initialization; Boolean-expression; step) {
statements;
}
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20. For Examples

for (int i = 10, k = 20; i < k; i++, k--) {
System.out.println(i + " " + k);
}
for (char i = 's'; i >= 'b'; i--) System.out.println(i);
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21. Break and Continue Statements

• break quits the loop without executing the rest of
the statements in the loop.
• continue stops the execution of the current iteration
and goes back to the beginning of the loop to begin
the next iteration.
• You can use a label before an iteration statement and
in break / continue statements interrupt the loops up
to where the label exists
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22. Use Break with a Label

L: for … {
for…{
break L;
}
}
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23. Exercise 2.2.1.

• Find and print all divisors of a given natural
number n.
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24. Exercise 2.2.1.

• See 221Divisors project for the full text.
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25. Exercise 2.2.2.

• Find and print all prime divisors of a given
natural number n.
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26. Exercise 2.2.3.

• Find sum of an infinite row for a given x
x x2
x3
xn
1
...
...
1
2!
3!
n!
• Compare result with a Math.exp(x) method
value
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27. Manuals

• Learning the Java Language. Language Basics
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