Printing, comments, and escapes

print vs println

Printing is how a program reports its results, and it is also how you will pass every exercise in this course: the checker compares your output character for character, so controlling exactly what appears — and where the line breaks fall — matters from day one. (Working engineers live in printed output too: server logs are millions of print statements.) Java gives you two printing tools:

• System.out.println(x) prints x and then moves to the next line.
• System.out.print(x) prints x and stays on the same line.

Comments work like this:

// single line comment, like Python's #
/* multi-line comment,
   like Python's triple quotes */

You can glue text and values together with +, the way you used + on strings in Python:

System.out.println("score: " + 42);

The + gotcha

+ means numeric addition between two numbers, but joining when either side is a String. Java evaluates left to right, so what happens depends on where the String enters the expression:

System.out.println("sum: " + 1 + 2);   // sum: 12
System.out.println("sum: " + (1 + 2)); // sum: 3
System.out.println(1 + 2 + " apples"); // 3 apples

In the first line, "sum: " + 1 joins into the String "sum: 1", and then + 2 joins again. Parentheses force the addition to happen first while both sides are still numbers. This bites real programs constantly — wrap arithmetic in parentheses whenever it shares a line with text.

Escape sequences

Inside a string, a backslash starts an escape sequence, a stand-in for a character you cannot type directly:

So System.out.println("a\nb") prints a and b on separate lines, exactly like Python's \n.