java – Do I have to use else?

Question:

Today I was at a Java interview and fell for the if .
The challenge was to write a method that returns the second largest number from the input array. Failed on the if while checking the data. My implementation was like this:

public int getSecondMaxNumber(int[] numbers) {
    if (numbers == null || numbers.length < 2) {
        throw new IllegalArgumentException();
    }
    // далее логика получения второго макс. числа
}

To my great surprise, it turned out that I had made a gross mistake. The program logic should be enclosed in an else block, that is, like this:

public int getSecondMaxNumber(int[] numbers) {
    if (numbers == null || numbers.length < 2) {
        throw new IllegalArgumentException();
    }
    else {
        // именно здесь логика получения второго макс. числа
    }
}

Why write all the rest of the code in the else block if the execution flow of this method is interrupted when an exception is thrown?

Similarly, as it turned out, and in the case when, instead of throwing an exception, return simply indicated. In general, there should always be an else after the if else .

As far as I understood from the words of the technical manager, in the case of the else JVM performs some kind of optimization. I would like to learn more about this moment – what kind of optimization and where can I read more about it?

Answer:

In addition to @ VladD's answer: I compiled the following class using java 8:

public class IfElse {
    public int getSecondMaxNumber1(int[] numbers) {
        if (numbers == null || numbers.length < 2) {
            throw new IllegalArgumentException();
        }
        return numbers[1];
    }

    public int getSecondMaxNumber2(int[] numbers) {
        if (numbers == null || numbers.length < 2) {
            throw new IllegalArgumentException();
        } else {
            return numbers[1];
        }
    }
}

You can see that the bytecode of the methods is exactly the same:

$ javap -c IfElse.class
Compiled from "IfElse.java"
public class IfElse {
  public IfElse();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public int getSecondMaxNumber1(int[]);
    Code:
       0: aload_1
       1: ifnull        10
       4: aload_1
       5: arraylength
       6: iconst_2
       7: if_icmpge     18
      10: new           #2                  // class java/lang/IllegalArgumentException
      13: dup
      14: invokespecial #3                  // Method java/lang/IllegalArgumentException."<init>":()V
      17: athrow
      18: aload_1
      19: iconst_1
      20: iaload
      21: ireturn

  public int getSecondMaxNumber2(int[]);
    Code:
       0: aload_1
       1: ifnull        10
       4: aload_1
       5: arraylength
       6: iconst_2
       7: if_icmpge     18
      10: new           #2                  // class java/lang/IllegalArgumentException
      13: dup
      14: invokespecial #3                  // Method java/lang/IllegalArgumentException."<init>":()V
      17: athrow
      18: aload_1
      19: iconst_1
      20: iaload
      21: ireturn
}