Try-with-resources

Java7 added the notion of AutoCloseable and the try-with-resources statement.

This statement allows us to provide a set of resources that would be automatically closed after the code is done with them. No more risk (or at least less risk) of forgetting to close a file.

Before Java7, that was a total mess:

BufferedReader br = null; // Nulls are bad, we know that
try {
    br = new BufferedReader(new FileReader("/some/peth"));
    System.out.println(br.readLine());
}
finally {
    if (br != null) { // Explicit check
        br.close(); // Boilerplate
    }
}

After Java7:

try (BufferedReader br = new BufferedReader(new FileReader("/some/peth"))) {
    System.out.println(br.readLine());
}

In Kotlin, the this statement is replaced with the use() function:

val br = BufferedReader(FileReader(""))

br.use {
    println(it.readLine())
}

...