Transcript public static void main (String [] args)

Laboratory Study
October, 17 2003
The very first example, traditional "Hello
World!" program:
public class first {
public static void main (String[ ] args) {
System.out.println("Hello World!");
}
}
 1.) Which line is the core of this phrase (program)?
Answer: This is an example of a statement, a phrase whose
execution causes an action to happen.
We could treat System.out.println (exp)1; as a magical line that
prints out the value of expression
1exp
is a phrase (known as an expression) that denotes a
value.
 2.) To write the simple Java program named first, which lines
are required?
• Answer:public class first {
public static void main (String [] args) {
::: }}
 3.) Write different screen outputs as
Java
Programming
Language
 4.) Write a variant of System.out.println as different
named System.out.print that displays the
given message, but does not go to the next line for message:
Java Programming Language
(not JavaProgrammingLanguage)
A Fibonacci Program
class Fibonacci {
public static void main (String args[ ]) {
int lo = 1;
int hi = 1;
System.out.println(lo);
while ( hi < 50 ) {
System.out.println(hi);
hi = lo + hi;
lo = hi - lo; } } }
 Type this code into the proper filename.
 Compile and run the program.
 Discuss the results.
Numerical Calculations
public class Numerical Examples {
public static void main (String [] args) {
System.out.print ("2 + 3.0 = ");
System.out.println (2 + 3.0);
System.out.print ("2 + 3 = ");
System.out.println (2 + 3);
System.out.print ("9.0 / 4 = ");
System.out.println (9.0 / 4);
System.out.print ("9 / 4 = ");
System.out.println (9 / 4); } }
The result is displayed as:
2 + 3.0 = 5.0
2+3=5
9.0 / 4 = 2.25
9/4=2
 Test the results of different arithmetic operations on your computer
console
String Concatenation
 Java's + operator is not only used to add numbers. It is also
used to concatenate two strings together. For example, the
expression:
"Java" + "line" denotes the 8-character string "Javaline".
 Using + for string concatenation can simplify programs by
reducing the number of calls to System.out.print and
System.out.println.
For example:
public class NumericalExamples {
public static void main (String [] args) {
System.out.print ("2 + 3.0 = " + (2 + 3.0));
System.out.print ("2 + 3 = " + (2 + 3));
System.out.print ("9.0 / 4 = " + (9.0 / 4));
System.out.print ("9 / 4 = " + (9 / 4); } }
 In previous example the parenthesis around
numerical expressions like (2 + 3.0) are required,
not
optional.
 If we instead wrote "2 + 3.0 = " + 2 + 3.0,
this would be parenthesized by Java as
("2 + 3.0 = " + 2) + 3.0
 By the coercion rules from above this would be
equivalent to ("2 + 3.0 = " + "2") + "3.0".
 So the displayed result would be
2 + 3.0 = 23.0
which is not at all what was intended!
Overloading of + operator
An operator like + that has different meanings in different contexts (e.g.,
add two integers vs. add two floating point numbers vs. concatenate two
strings) is said to be overloaded.
Expression
is treated as
whose value is
42 + 3.141
42.0 + 3.141
45.141
"42" + 3.141
"42" + "3.141“
"423.141"
42 + "3.141"
"42" + "3.141"
“423.141"
63 + -273.15
63.0 + -273.15
-210.15
"63" + -273.15 "63" + "-273.15"
"63-273.15"
63 + “-273.15" "63" + "-273.15"
"63-273.15
 Show this representations on your computer
console
Naming Values Via Variables
An example program indicating variable operations:
public static void main (String [ ] args) {
double a = 10.27;
double b = 8.56;
double a_squared = a*a;
double b_squared = b*b;
System.out.println ((a_squared + b_squared) / (a_squared - b_squared));
}
Another version of the above program can be written as follows::
public static void main (String [] args) {
double a = 10.27;
double b = 8.56;
double a_squared = a*a;
double b_squared = b*b;
double sum = a_squared + b_squared
double diff = a_squared - b_squared
double quot = sum/diff
System.out.println(quot); }
Series Summation Program
An arithmetic series is a series of n integers
i1, i 2 ,….…in where each element is greater than the
previous element by the same value d.
For instance, here are some examples of arithmetic series:
Series
6;7; 8; 9; 10; 11; 12
2; 4; 6; 8
6; 11; 16; 21; 26; 31; 36; 41
n
7
4
8
i1
6
2
6
in
12
8
41
d
1
2
5
 The sum of such a series is the number of pairs of
elements multiplied by the sum of the first and last
elements:
n /2 (i1 + i n).
 Suppose that we are not given n, but are given the
first and last elements of the series and the
difference d between consecutive elements.
Then we can calculate n as :
( (in - i1) / d ) + 1
 For
instance, for series with first element 6,
last element 41 and difference 5,
n = (41-6) / 5 +1 = 8.
 Write a Java program for calculating the sum of the more
general form of an arithmetic series.