Python and Java - Comparisons and Contrasts

Python and Java are the same here.

In Python, standard library functions usually have lowercase names.

In Java, standard library functions usually have "camelCase" names (each word but the first begins with a capital letter).

Python: Can run any file in the project.

Java: Must have a class in the project that defines a main() method.

Executes the code in order from beginning to end of the file.

main() is optional, and has no special meaning in Python.

That means that Java starts in the class in the project containing main(), but main() can call methods from other classes.

main() needs to be declared as public static void main in Java to work.

   public static void main(String[] args) {
	 // body of main()
   }

Java interprets /** as beginning a documentation string; Python interprets the first string of a function/class/method (usually set aside with triple quotes) as its documentation.

The following is illegal:

/* cannot have /* comment inside */ comment */

x = f(a, b);

double x;

...
x = 5.6; // legal
x = "String value"; 
/* This is illegal in Java; types don't match*/	

int i;
int n = 5;
double x=7.3, y=8.2, z;
				

try:
	<code that could throw an exception>
except:
	<code to handle the exception>
				

try {
	<code that could throw an exception>
}
catch (ExceptionType e) {
	<code to handle the exception>
}
				

sum = 0

for i in range(5):
	sum += i
print i, sum
	 			

int i, sum=0;
for (i=0; i<5; i++) {
	sum += i;
}

System.out.print(i);
System.out.print(' ');
System.out.println(sum);
				

for <variable> in <list>:
	 <one or more indented statements>
	 			

for (<initialization> ; <test>; <update>) {
	 <zero or more body statements>
}  

for (int i : numList) {
	 <zero or more body statements>
}
				

initialization: usually gives initial value to loop variable(s)

test: If the value of the test is true, the loop continues.

update: After each execution of the loop body, this code is executed, and the test is run again.

The second form of the for loop works for the elements of an array,

In Java, a block can be used anywhere a single statement can be used.

If a Java block only contains one statement, the braces are optional.

for (<initialization> ; <test>; <update>) 
	 <statement>
	 			

while <condition>:
	<one or more indented statements> 
				

while ( <condition> )
	<statement>
				

if <condition>:
	<one or more indented statements> 
				

if ( <condition> )
	<statement>
				

if <condition>:
	<one or more indented statements>
else:
	<one or more indented statements> 
				

Java Syntax is just like C.
 

if <condition>:
	<one or more indented statements>
elif <condition>:
	<one or more indented statements>
else:
	<one or more indented statements> 
				

if ( <condition> )
	<statement>
else if ( <condition> )
	<statement>
else
	<statement>
				

Java Syntax is just like C.
 

switch (<variable>) {
	case <value1> :
		<statement1>
		break;
	case <value2> :
		<statement2>
		break;
	...
	default:
		<statement>
}
				

Java Syntax is just like C.
 

Python has nothing that is like Java's switch statement ( if-elif-else is used)

If there are multiple statements for a given case, no curly braces are needed.

Don't forget the break; at the end of each case (except the last).

public static int max (int a, int b) {
   return (a > b) ? a : b;
}

Java Syntax is just like C.

int type is typically 32-bit.

long type is sometimes 64-bit, but always at least 32-bit.

There is no automatic conversion of values.

Note that Java has an ArrayList class with much of the functionality of Python's lists, but no special list syntax like Python has.

print 5,

print "x =" , 5

System.out.print(5);

System.out.println("x = " + 5);

In Python, print is a keyword, which can take a list and prints the elements of the list one at a time.

In Java, the print and println methods take a single argument. To print multiple things with one call, you need to convert them all to strings and concatenate the strings.

 def move(self, deltax, deltay):
     self.x += deltax
     self.y += deltay

  int move(int deltax, int deltay){
     this.x += deltax;
     this.y += deltay;
  }

from math import *

def printRootTable(n):
	for i in range(1,n):
		print " %2d %7.3f" % (i, sqrt(i))

def main():
	printRootTable(10)

main()

public class RootTable {
	public static void printRootTable(int n) {
		int i;
		for (i=1; i<=n; i++) {
			System.out.printf(" %2d %7.3f\n", i, Math.sqrt(i));
		}
	}
	
	public static void main(String args[]) {
	      RootTable.printRootTable(10);
	}
}

m,n = input("Enter two numbers: ")
print m, n

import java.util.Scanner;

public class InputTwo {
	public static void main(String args[]) {
		int i, j;
		System.out.print("Enter two numbers: ");

		Scanner s = new Scanner(System.in)

		i = s.nextInt();
		j = s.nextInt();

		System.out.print(i);
		System.out.print(' ');
		System.out.println(j);
	}
}