Java Wrapper Classes — Free Java Tutorial

TL;DR: Learn Java Wrapper Classes in Java with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Java Wrapper Classes in Java

Every primitive type in Java has a corresponding Wrapper class: int → Integer, double → Double, boolean → Boolean, char → Character, long → Long, etc.

Wrapper classes turn primitives into objects, enabling them to be stored in Collections (List, Map, etc.) which require objects, not primitives.

Autoboxing is the automatic conversion from primitive to wrapper (int → Integer). Unboxing is the reverse (Integer → int). Java does this transparently.

Wrapper classes provide useful static utility methods: Integer.parseInt(), Double.parseDouble(), Integer.toBinaryString(), Integer.MAX_VALUE, Integer.MIN_VALUE.

Null handling: a wrapper variable can be null (unlike a primitive). Unboxing a null Integer throws NullPointerException.

// Autoboxing
Integer a = 42;         // int -> Integer (autoboxing)
int b = a;              // Integer -> int (unboxing)

// Useful methods
int n = Integer.parseInt("123");
String s = Integer.toString(456);
int max = Integer.MAX_VALUE;  // 2147483647

// Collections require wrappers
List<Integer> l

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