Stage 1 · Lesson 2 of 9
Types, variables and input
Java is : every has a type that is fixed when the code is compiled, such as int age = 20 or String name = "Ada". The types (int, long, double, boolean, char) hold their values directly. Everything else, String included, is a reference that points to an object.
cuts off the decimal part, so 7 / 2 is 3. An int also silently overflows (wraps around) past about 2.1 billion. var lets the compiler work out a local variable's type for you, which is called type inference, but that type is still fixed.
Each primitive has a wrapper class, such as Integer, which is used in collections, and a wrapper can be null. Read with Scanner. Convert text with Integer.parseInt, which throws NumberFormatException on "abc".
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Resources for this stage
Start with· follow one of these
- CourseFreeJava Programming MOOC
University of Helsinki · Beginner
Free Helsinki course with hundreds of auto-tested exercises; parts 1 to 8 cover this stage
- GuideFreeDev.java: Learn Java
Oracle · Beginner
Official tutorials from the Java team: read the language basics path next to the MOOC