Scala2e Chapter5 Basic Types and Operations 5.7 Object equality

If you want to compare two objects for equality, you can use either ==, or its inverse !=.

scala> 1 == 2

res31: Boolean = false

scala> 1 != 2

res32: Boolean = true

scala> 2 == 2

res33: Boolean = true

scala> List(1, 2, 3) == List(1, 2, 3)

res34: Boolean = true

scala> List(1, 2, 3) == List(4, 5, 6)

res35: Boolean = false

scala> 1 == 1.0

res36: Boolean = true

scala> List(1, 2, 3) == "hello"

res37: Boolean = false

scala> List(1, 2, 3) == null

res38: Boolean = false

scala> null == List(1, 2, 3)

res39: Boolean = false

This kind of comarison will yield true on different objects, so long as their contents are the same and their equals method is written to be based on contents.

scala> ("he"+"llo") == "hello"

res40: Boolean = true

In Java, you can use == to compare both primitive and reference types.

On primitive types, Java's == compares value equality, as in Scala. 

On reference types, however, Java's == compares reference equality, which means the two variables point to the same object on the JVM's heap.

Scala provides a facility for comparing reference equality, as well, under the name eq. However, eq and its opposite, ne, only apply to objects that directly map to Java objects.