Kotlin
Kotlin
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Object Expressions and Declarations

Object Expressions and Declarations

Sometimes we need to create an object of a slight modification of some class, without explicitly declaring a new subclass for it. Java handles this case with anonymous inner classes. Kotlin slightly generalizes this concept with object expressions and object declarations.

Object expressions

To create an object of an anonymous class that inherits from some type (or types), we write:

window.addMouseListener(object : MouseAdapter() {
    override fun mouseClicked(e: MouseEvent) {
        // ...
    }

    override fun mouseEntered(e: MouseEvent) {
        // ...
    }
})

If a supertype has a constructor, appropriate constructor parameters must be passed to it. Many supertypes may be specified as a comma-separated list after the colon:

open class A(x: Int) {
    p