Java static methods lab



In this exercise, you will learn to write static methods that use Lists and Strings. Each of these is around the difficulty of some exam questions. If you need to make a new List as part of the method, implement it using an ArrayList.


Static Generic Methods Java makes writing generic methods look intimidating, but, it’s not so bad. I'll walk you through how to do it by showing what we want to do, encountering an exception, and then showing you how to resolve the exception


Suppose we want to write a method called in that checks if the List contains a specified item. We don't know, in advance, what type the item will be nor do we know the type of the items in the List. We also want this method to be able to be used in any kind of context. That means we want it to be generic. However, if we write


public static boolean in(List list, E item) {




we get a compile time exception: “E cannot be resolved to a type” because Java doesn’t know that you want to use E as the symbol for generics in this method. We can inform the compiler of our intention by including the generic symbol before the method’s return type.


public static Boolean in(List list, E item) {




The big difference between a class that uses a generic, like ArrayList, and the static methods you write for this assignment is that the generic type only exists for the method.

Specifications For each of the following, create a static method with the appropriate inputs and outputs. Call each of them in the main method.

Uniqueness Write a method unique() which returns true if all the items in the supplied List are unique. All the items are unique if none of them are the same. Return false otherwise.


All Multiples Write a method allMultiples() which returns a new List of integers that contains all of the integers in the List argument that are multiples of the given int. For example, if the List is [1; 25; 2; 5; 30; 19; 57; 2; 25] and 5 was provided, the new list should contain [25; 5; 30; 25].


All Strings of Size Write a method named allStringsOfSize() which returns a new List which contains all the Strings from the List argument that are length characters long. For example, if the inputs are ["I", "like", "to", "eat", "eat", "eat", "apples", "and", "bananas"] and 3, the new list is ["eat", "eat", "eat", "and"].


Permutations Write a method isPermutation() which return true if the two List arguments are permutations of each other, otherwise it returns false. Two lists are permutations if they contain the same elements, including the same number of duplicates, but they don't have to contain the elements in the same order. For example, [1,2,4] and [2,1,4] are permutations of each other.


String Tokenization1 Write a method tokenize() returns a List of words from the input string. We assume that each word in the input string is separated by whitespace.2 If our input String is "Hello, world!", then the output should be ["Hello,", "world!"]


Remove All Write a method removeAll() which removes all of the specified items from the List and returns the new List. For example, if the method is passed the List [1, 4, 5, 6,5, 5, 2] and the Integer 5, the method removes all 5's from the List. The List then becomes [1, 4, 6, 2]

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