info.michael-simons.eu

Someone must be hit really hard with some curly braces when he implemented the following behaviour:

public class Braindead {
	public static void main(String[] args) {
		Integer i1 = 10;
		Integer i2 = 10;
 
		Integer i3 = 128;
		Integer i4 = 128;
 
		compare(i1, i2);
		compare(20, 20);
		compare(i3, i4);
	}
 
	public static void compare(Integer i1, Integer i2) {
		System.out.println("Comparing " + i1 + " and " + i2);
 
		if(i1 == i2)
			System.out.print("same ");
		else
			System.out.print("different ");
		System.out.println("Objects");
 
		if(!i1.equals(i2))
			System.out.print("not ");
		System.out.println("meaningfully equal");
		System.out.println("---");
	}
}

I’d expect the following output:

Comparing 10 and 10
different Objects
meaningfully equal
---
Comparing 20 and 20
different Objects
meaningfully equal
---
Comparing 128 and 128
different Objects
meaningfully equal
---

What you get is:

Comparing 10 and 10
same Objects
meaningfully equal
---
Comparing 20 and 20
same Objects
meaningfully equal
---
Comparing 128 and 128
different Objects
meaningfully equal
---

In order to save memory, two instances of the following wrapper objects will always be == when their primitive values are the same:

• Boolean
• Byte
• Character from \u0000 to \u007f
• Short and Integer from -128 to 127

So in order to save a handfull of bytes we present you some really inconvenient feature 😉