How to retrieve a variable name given its value?

Given that an ArrayList named a whose elements are of type int has been declared assign the value -1?

• I've been having trouble figuring out these erros. Any help is greatly appreciated!! :) 1) Given that an ArrayList named a whose elements are of type int has been declared, assign the value -1 to the last element in a . My answer (Unexpected identifiers: get): a.get(a.size() - 1, -1); 2) Assume that an ArrayList of Integer s named a that contains exactly five elements has been declared and initialized. In addition, an int variable j has also been declared and initialized to a value somewhere between 0 and 3 . Write a single statement that assigns a new value to element of the ArrrayList indexed by j . This new value should be equal to twice the value stored in the next element of the ArrayList (i.e. the element after the element indexed by j . My answer (error:  Unexpected identifiers: length) : a.set(0, 2*(a.get(a.length - 1))); 3)The superclass Student contains: a constructor that accepts a String corresponding to the name of the school the student attends a toString method that returns 'student at X' where X is the name of the school the student attends. Write a class definition for the subclass HighSchoolStudent containing: a constructor accepting a String which is used as a parameter to the superclass constructor a toString method that returns 'high school student at X'. This method must use the toString method of its superclass. My answer (error said  expected but did not find a (default-access) constructor accepting a java.lang.String parameter.) : class HighSchoolStudent extends Student{ public HighSchoolStudent(String X) { super(X); } public String toString() { return "high school student at" + super.toString(); } }

• Answer:

  1) The get method doesn't set anything, it only returns the value at the given index. You're looking for the set method. The set method takes in an int index and an object to set at that index. So you'd want a.set(a.size()-1, -1); 2) You want a new element at index j, that has the value of two times the element at index j+1. So you're looking for: a.set(j, 2*(a.get(j+1)));