2. Java Basics. Java Statements презентация

2. Java Basics 2. Java Statements

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

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 fields Java associates documentation comments with the first declaration after the comment

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.

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); } }

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); } } }

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); } }

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); } } }

Constant Declaration final modifier: final int a = 42; // a = 12; - compile error

If-Then_Else Statement I if (boolean_expression) { statements } if (boolean_expression) { statements } else { statements }

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

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"); }

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

Switch Example char c = ’b’; switch(c) { case ’a’: case ’e’: case ’i’: case ’o’: case ’u’: print("vowel"); break;

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!)

While and Do-While Statement while (boolean_expression) { statements; } do { statements; } while (boolean_expression);

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

Do-While Example double a = 0.5; do { System.out.println(a); a /= 2.; } while (a >= 1);

For Statement for (initialization; Boolean-expression; step) { statements; }

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);

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

Use Break with a Label L: for … { for…{ break L; } }

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

Exercise 2.2.1. See 221Divisors project for the full text.

Exercise 2.2.2. Find and print all prime divisors of a given natural number n.

Exercise 2.2.3. Find sum of an infinite row for a given x Compare result with a Math.exp(x) method value

Manuals Learning the Java Language. Language Basics