Java Comments
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// single-line comment
/* multi-line
comment */
/** Javadoc comment */Single-Line Comments
A // comment runs from that point to the end of the line, making it ideal for short, one-line notes explaining a tricky piece of logic right next to the code it describes.
Example: Single-Line Comments
public class Main {
public static void main(String[] args) {
int total = 100; // running total for the cart
System.out.println(total);
}
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Multi-Line Comments
A /* ... */ block comment can span multiple lines, which is useful for temporarily disabling a chunk of code or writing a longer explanation above a complex method.
Example: Multi-Line Comments
public class Main {
/*
* This block comment can span
* multiple lines of explanation.
*/
public static void main(String[] args) {
System.out.println("See the block comment above.");
}
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Javadoc Comments
Javadoc comments (/** ... */) placed above a class or method get picked up by the javadoc tool to auto-generate browsable HTML API documentation -- this is how Java's own standard library docs are built.
Example: Javadoc Comments
public class Main {
/**
* Adds two integers together.
* @param a first number
* @param b second number
* @return the sum of a and b
*/
static int add(int a, int b) {
return a + b;
}
public static void main(String[] args) {
System.out.println(add(2, 3));
}
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Commenting Out Code
Wrapping code in // or /* */ during debugging lets you quickly rule out whether a specific block is causing a bug, without deleting and having to retype it afterward.
Example: Commenting Out Code
public class Main {
public static void main(String[] args) {
System.out.println("Active line");
// System.out.println("Disabled while debugging");
}
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Comment Best Practices
Stale comments that no longer match the code they describe are worse than no comment at all, since they actively mislead the next reader -- update or delete them whenever you change the logic nearby.
Example: Comment Best Practices
public class Main {
public static void main(String[] args) {
int price = 20; // price in dollars (kept in sync with the code beside it)
System.out.println(price);
}
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- Writing a
/* ... */comment inside another/* ... */, since block comments do not nest and the first*/ends it. - Forgetting to close
/*so the rest of the file becomes a comment. - Using
#or--for comments as in other languages, when Java uses//and/* */.
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