🔄 Foundations

Java Fundamentals — Quick Review

⏱ 3 hr4 topicsInteractive

🎯 By the end: You can recall Java's basic building blocks — data types, operators, input, Math methods, conditionals and loops — ready to build on with classes and methods.

This chapter is a refresher of the Java you met in Class 9, so the new Class 10 topics build on solid ground. Java is an object-oriented language: programs are built from objects created from classes. (Java code here is for you to read and run in BlueJ/an IDE — it can't run inside the browser.)

1OOP, objects and classes

Object-Oriented Programming (OOP) models a program as a set of objects that hold data and can act on it. An object is a real-world thing (a student, a car); a class is the blueprint that describes what such objects have and can do.

class Student {        // the blueprint (class)
  String name;         // data the object holds
  int marks;
}

Student s = new Student();   // s is an object of class Student

A class is like a cookie-cutter; objects are the cookies. One class can make many objects.

Key points

Java is object-oriented: programs are built from objects created from classes.
An object is a specific thing; a class is the blueprint describing such things.
One class can create many objects using the new keyword.

2Data types, variables and operators

A variable stores a value; its data type says what kind. Java's common primitive types:

Type	Holds	Example
`int`	Whole numbers	int age = 15;
`double`	Decimal numbers	double pi = 3.14;
`char`	One character	char g = 'A';
`boolean`	true / false	boolean ok = true;

Operators combine values:

Arithmetic: + - * / % (% is remainder)
Relational: < > <= >= == !=
Logical: && (and), || (or), ! (not)

Key points

Common primitive types: int (whole), double (decimal), char (one character), boolean (true/false).
Arithmetic operators: + - * / and % (remainder).
Relational (<, >, ==, !=) compare; logical (&&, ||, !) combine true/false values.

3Input and Math library methods

To read input from the user, Java uses the Scanner class:

import java.util.Scanner;

Scanner sc = new Scanner(System.in);
int n = sc.nextInt();        // read a whole number
String s = sc.next();        // read a word

Math methods

The Math class provides ready-made calculations:

Method	Returns
`Math.sqrt(x)`	Square root
`Math.pow(a, b)`	a to the power b
`Math.abs(x)`	Absolute (positive) value
`Math.max(a, b)` / `Math.min(a, b)`	Larger / smaller

Key points

Scanner (from java.util) reads input: nextInt() for a number, next() for a word.
The Math class has ready calculations: sqrt, pow, abs, max, min.
Math methods are called on the class name, e.g. Math.sqrt(25).

4Decisions and loops

Conditional statements choose what to do:

if (marks >= 33)
  System.out.println("Pass");
else
  System.out.println("Fail");

switch (grade) {
  case 'A': System.out.println("Great"); break;
  default:  System.out.println("Keep going");
}

Loops repeat actions:

for (int i = 1; i <= 5; i++)      // runs 5 times
  System.out.println(i);

int i = 1;
while (i <= 5) { i++; }            // entry-controlled

do { i++; } while (i <= 5);        // exit-controlled (runs at least once)

A nested loop is a loop inside another loop — used for grids, tables and patterns.

Key points