2. Java Basics
Comments
How to Use Comments
Variables
1. What will this program output?
2. What will this program output?
3. What will this program output?
4. What will this program output?
Constant Declaration
If-Then_Else Statement I
If-Then_Else Statement II
If-Then-Else Example
Switch Statement
Switch Example
Switch Statement Expressions
While and Do-While Statement
While Example
Do-While Example
For Statement
For Examples
Break and Continue Statements
Use Break with a Label
Exercise 2.2.1.
Exercise 2.2.1.
Exercise 2.2.2.
Exercise 2.2.3.
Manuals
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Категория: ПрограммированиеПрограммирование

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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