CSDS 123 Midterm

How is data represented on a computer?

All data is just numbers (bits 0’s and 1’s)

What is the type of a value?

what a piece of data represents

How does Java use types?

to store numeric values/ data

What are the rules Java uses to determine the types resulting from primitive operators?

Java automatically widens the narrower type then executes the expression.

Strongly Typed

every value in program has an unambiguous type

What are the differences between a value that is a primitive type and a value that is a non-primitive type?

Primitive type values are the data themselves

Non-primitive types reference memory location where the data is stored.

What is the purpose of a typecast?

convert data to different types

When are typecasts done automatically?

Typecasts are done automatically when going from a narrower to a wider type. This is called widening.

When must a typecast be explicit?

When going from a wider type to a narrower type. This is called narrowing.

When are typecasts illegal?

they violate the type compatibility rules (Ex: String to int)

How does a typecast affect a value of primitive type?

Typecasting temporarily changes the type of a value to the type casted

What is null?

a value that shows the object is referring to nothing

What is “short circuit evaluation“ and what operators use it?

Evaluation of a logical expression stops before a complete evaluation. (&& and ||)

What ways do a arithmetic on a computer differ from “real“ arithmetic

Errors will crop up due to the fixed size of the numeric data types

What are variables

A variable is a name given to a location in memory.

Difference between declaring and assigning a variable

• Declaring creates a variable

• Assigning assigns a value to an already created variable

Where can a variable be accessed?

Using expressions

How long does a variable exist

• An instance variable exists as long as the class that it is in exists.

• A local variable exists as long as the method that it is in also exists.

• input parameters only exists until after the method that it is in is called.

What is the difference between static and non-static fields

• Static variables are shared among all instances of a class

• Non static variables are specific to that instance of a class

What is the difference between static and non-static methods

• A static method is a class method and belongs to the class itself

• non-static method is an instance method and belongs to each object that is generated from the class

What does public and private do

Public : can be accessed anywhere

Private: direct access only within this type

What does protected do

can be accessed by code in same folder or types that are protected

What does final do

means that the value, once set, will not change.

What are the parameters of a method and how do they work?

Takes input and utilizes them within methods

What is the return value?

values the function returns when it completes

method overloading

multiple methods/constructors of the same name as long as they have different inputs

method overriding

occurs when a subclass has the same method as the parent class

What is ‘this‘

refers to the current object in a method or constructor

What is super

refers to the superclass (parent) objects, used to call superclass methods

When is super() & this() used

• super() can access the parent class constructor

• this() can access current class constructor

What strategies should I use to test a method with a loop

JUnit, or creating tester methods

How do you create a string

String name = new String(“hello“) or String name = “hello“

How do you concatenate strings

Stringbuilder

What is a StringBuilder and when do we use it

Used when we want to modify a string without creating a new object

What can you change about a string after you create it

Nothing (String are immutatble)

What is an array

container object that holds a fixed number of values of a single type

How do you create an array

int intArray[] = new int[20];

benefits of a array

Very fast access to every elements and organizes data

Strictly Typed

It is an error to use a type with an operation not valid on that type