Java Syntax & Structure
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public class ClassName {
public static void main(String[] args) {
statement; // each statement ends with ;
}
}Case Sensitivity
Java treats uppercase and lowercase letters as entirely different characters, so myVariable and MyVariable are two distinct identifiers -- this trips up beginners coming from case-insensitive languages.
Example: Case Sensitivity
// Define the class Main
public class Main {
// Program entry point: the JVM starts running here
public static void main(String[] args) {
// Declare myVariable and set it to 1
int myVariable = 1;
// Declare MyVariable and set it to 2
int MyVariable = 2;
// Print a line to the console
System.out.println(myVariable + " and " + MyVariable + " are different variables.");
}
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Curly Braces
Every class body, method body, loop, and conditional block is delimited by a matching pair of curly braces, and a missing or misplaced brace is one of the most common compiler errors you'll encounter.
Example: Curly Braces
// Define the class Main
public class Main {
// Program entry point: the JVM starts running here
public static void main(String[] args) {
// Check whether true
if (true) {
// Print a line to the console
System.out.println("Inside the if block");
}
}
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Class Naming Conventions
Convention (enforced by tooling, not the compiler) says class names use PascalCase, capitalizing the first letter of each word, like BankAccount or HttpClient -- following it keeps your code readable to other Java developers.
Example: Class Naming Conventions
// Define the class BankAccount
class BankAccount {
double balance;
}
// Define the class Main
public class Main {
// Program entry point: the JVM starts running here
public static void main(String[] args) {
// Create a new BankAccount object and store it in account
BankAccount account = new BankAccount();
// Print a line to the console
System.out.println("Class named in PascalCase: BankAccount");
}
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Method Naming Conventions
Method names follow camelCase instead, starting lowercase, like calculateTotal() -- this visual distinction from PascalCase class names helps you tell at a glance whether an identifier is a type or a behavior.
Example: Method Naming Conventions
// Define the class Main
public class Main {
static int calculateTotal(int a, int b) {
// Send a + b back to the caller
return a + b;
}
// Program entry point: the JVM starts running here
public static void main(String[] args) {
// Print a line to the console
System.out.println("Method named in camelCase: " + calculateTotal(2, 3));
}
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Indentation and Whitespace
The compiler doesn't care how you indent your code, but consistent indentation (typically 4 spaces per nesting level) is what makes deeply nested loops and conditionals actually readable to a human.
Example: Indentation and Whitespace
// Define the class Main
public class Main {
// Program entry point: the JVM starts running here
public static void main(String[] args) {
// Loop: repeat while the condition holds
for (int i = 0; i < 2; i++) {
// Print a line to the console
System.out.println("Consistently indented nested block: " + i);
}
}
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- Using the wrong case, such as
stringinstead ofString, since Java is case-sensitive. - Forgetting to close a curly brace, so the compiler reports an error at the end of the file rather than where the brace is missing.
- Leaving out the semicolon at the end of a statement, which gives
';' expected.
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