JavaPlay

Learn Java syntax, then build what you want.

Read, run and fix real Java, one step at a time, on the way to classes, arrays, ArrayList and recursion. Code runs right in your browser.

Start here ☕ println or print? First Java

Units

1. ☕ 1 First Java
   • class
   • main
   • System.out.println
   • System.out.print
   • int
   • double
   • boolean
   • String
   • (int)
   • /
   • %
   🛠 A unit converter 0 / 10
2. 🧰 2 Using Objects
   • new
   • length()
   • substring()
   • indexOf()
   • charAt()
   • equals()
   • Math.pow()
   • Math.sqrt()
   • Integer.parseInt()
   • null
   🛠 A name and text formatter 0 / 10
3. 🔀 3 Decisions
   • if
   • else
   • else if
   • &&
   • ||
   • !
   • ==
   • !=
   • ? :
   🛠 A grade and ticket calculator 0 / 9
4. 🔁 4 Loops
   • while
   • for
   • ++
   • +=
   • nested for
   • break
   • continue
   • charAt(i)
   🛠 A pattern printer and a number game 0 / 10
5. 🧩 5 Methods
   • static
   • return
   • void
   • parameters
   • overloading
   • scope
   🛠 A small math toolkit 0 / 10
6. 🏗️ 6 Classes
   • class
   • new
   • constructor
   • this
   • private
   • getter
   • setter
   • toString
   • static field
   🛠 A bank account and a student record 0 / 10
7. 🧮 7 Arrays
   • int[]
   • new int[n]
   • {1, 2, 3}
   • .length
   • a[i]
   • for-each
   • int[][]
   🛠 A gradebook and a game board 0 / 11
8. 📋 8 ArrayList & Data
   • ArrayList<E>
   • add
   • get
   • set
   • remove
   • size
   • Integer
   • File
   • Scanner
   • throws IOException
   • sorting
   🛠 A class roster read from a file 0 / 12
9. Coming next: 9 Recursion