Java Primitive Types and Objects Cheat Sheet

The core ideas of Java Primitive Types and Objects distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Primitive Data Types

Eight types: int (32-bit), double (64-bit float), boolean (true/false), char (16-bit Unicode), byte, short, long, float. Store values directly in memory.

Reference Types and Objects

Store memory addresses pointing to heap objects. Can hold null. Assignment copies the reference, not the object.

The String Class

Immutable character sequence. Methods: length(), substring(), indexOf(), equals(), compareTo(). Modification returns new Strings.

Type Casting

Widening (int to double) is automatic. Narrowing (double to int) requires explicit cast and truncates.

The Math Class

Static methods: abs(), pow(), sqrt(), random()[0.0,1.0), min(), max().

Integer Division and Modulus

Both int operands: truncates decimal. Modulus (%) returns remainder.

Autoboxing and Unboxing

Auto-conversion between primitives and wrappers (int/Integer). Enables primitives in ArrayList.

Key Terms at a Glance

Primitive Type:One of eight basic Java types storing values directly in memory.

Reference Type:Variable storing memory address to heap object.

Widening Conversion:Automatic conversion from smaller to larger type.

Narrowing Conversion:Explicit conversion from larger to smaller type.

Type Casting:Converting between types using (targetType) syntax.

String:Immutable character sequence class in Java.

Autoboxing:Auto primitive to wrapper conversion.

Unboxing:Auto wrapper to primitive conversion.

String Pool:Memory area where identical literals share one object.

NullPointerException:Runtime exception from null reference usage.

Modulus (%):Remainder of integer division.

Compound Assignment:Operators like += and *= combining operation with assignment.

Math Class:Static methods: abs, pow, sqrt, random, min, max.

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