Implementing an interface in Java - Why does javap output two methods with the same signature but different return type?

Question

Given this Java code:

interface I {
  Object getId();
}

class A implements I {
  public Long getId() {
    return null;
  }
}

javac I.java A.java

It compiles successfully. When disassembled the class files produces the following output:

javap I.class
javap A.class

Compiled from "I.java"
interface I {
  public abstract java.lang.Object getId();
}

Compiled from "A.java"
class A implements I {
  A();
  public java.lang.Long getId();     <--- (1)
  public java.lang.Object getId();   <--- (2)
}

Question is why two methods with the same signature (1) & (2) are present in the disassembled output ? Having two methods with the same signature - isn't it not something JLS disallows ?