Understand the idea

Wrapper classes such as Integer represent primitive-like values as objects. Autoboxing and unboxing make many conversions implicit, which is convenient for collections. Null references and object identity can still surprise you.

Explore the details

Java Wrapper Classes

Wrapper classes provide a way to use primitive data types (int, boolean, etc..) as objects.

The table below shows the primitive type and the equivalent wrapper class:

Sometimes you must use wrapper classes, for example when working with Collection objects, such as ArrayList, where primitive types cannot be used (the list can only store objects):

Creating Wrapper Objects

To create a wrapper object, use the wrapper class instead of the primitive type. To get the value, you can just print the object:

Since you're now working with objects, you can use certain methods to get information about the specific object.

For example, the following methods are used to get the value associated with the corresponding wrapper object: intValue(), byteValue(), shortValue(), longValue(), floatValue(), doubleValue(), charValue(), booleanValue().

This example will output the same result as the example above:

Another useful method is the toString() method, which is used to convert wrapper objects to strings.

// Auto-boxing: primitive → wrapper (automatic)
int num = 42;
Integer boxed = num;   // autoboxing
int unboxed = boxed;   // unboxing

// Useful static methods
System.out.println(Integer.MAX_VALUE);          // 2147483647
System.out.println(Integer.MIN_VALUE);          // -2147483648
System.out.println(Integer.parseInt("123"));     // 123
System.out.println(Double.parseDouble("3.14")); // 3.14
System.out.println(Integer.toBinaryString(10)); // 1010

// Convert wrapper to String
String s = Integer.toString(255);
System.out.println(s.length()); // 3  (length of "255")

In the following example, we convert an Integer to a String, and use the length() method of the String class to output the length of the "string":

A complete runnable example

This complete Main.java program focuses on the lesson idea. Reference fragments above may demonstrate individual statements; this example includes the imports, entry point, and supporting types it needs.

public class Main {
    public static void main(String[] args) throws Exception {
        int value = 42;
        Integer boxed = value;
        int unboxed = boxed;
        System.out.println(unboxed);
        System.out.println(Integer.parseInt("125") + 5);
    }
}

42
130

Change it. Run it. Understand it.

Load this lesson example into the editor. Change one value or statement, predict the result, then press RUN to execute Java.

Make it your own

Your learning checkpoint

• Explain the example without reading the output first.
• Make the change requested in the practice task.
• Describe why the result changed—or why compilation failed.

Ready to move on? Follow the next lesson in course order, or return to the curriculum to review a prerequisite.