Java Objects Basics Quiz

In Objects-First learning, what is the blueprint that defines state and behaviour for objects?

• Object
• Class
• Field
• Method
• Package

Answer explanation

A class defines the fields (state) and methods (behaviour); objects are instances.

In Circle, which of the following are part of the state?

• diameter
• xPosition
• isVisible
• draw()
• moveRight()

Answer explanation

State is stored in fields; draw()/moveRight() are behaviours (methods).

Guess the concept name: “A block of code defined in a class that can make an object act and may change its fields.”

• Field
• Constructor
• Behaviour (method)
• Package
• Type

Answer explanation

Behaviours are methods; they can change the object’s state.

Immediately after Circle c = new Circle(); (no other calls), what is c.color?

• "red"
• "blue"
• "green"
• null
• "black"

Answer explanation

The default constructor sets color = "blue".

After Square s = new Square(); s.moveLeft(); s.moveUp();, what are (xPosition, yPosition)?

• (330, 140)
• (310, 120)
• (290, 100)
• (290, 120)
• (310, 100)

Answer explanation

Start (310,120). Left → x=290; Up → y=100.

Which actions directly change state without needing extra information?

• moveRight()
• moveHorizontal(int distance)
• makeVisible()
• changeColor(String)
• moveDown()

Answer explanation

moveRight()/moveDown() have fixed deltas; makeVisible() flips isVisible. Others need parameters.

Guess the meaning: In this chapter’s context, “state change” primarily means…

• Modifying method signatures
• Changing the values of the object’s fields
• Creating a new instance
• Compiling the project
• Importing a package

Answer explanation

State is represented by field values; changing them changes the state.

For Triangle t = new Triangle();, which tuple is correct initially? (height, width, xPosition, yPosition, color, isVisible)

• (60, 70, 210, 140, "green", false)
• (70, 60, 210, 140, "green", true)
• (60, 60, 230, 90, "blue", false)
• (60, 70, 210, 140, "red", false)
• (60, 70, 230, 90, "green", false)

Answer explanation

Matches constructor defaults in Triangle.

In Person, which are behaviours that require extra information from the caller?

• changeSize(int newHeight, int newWidth)
• changeColor(String newColor)
• moveVertical(int distance)
• moveLeft()
• makeInvisible()

Answer explanation

These methods take parameters and directly update fields; others don’t.

Consider: Circle c = new Circle(); c.makeVisible(); c.moveHorizontal(15); c.moveHorizontal(-5); Final xPosition?

• 230
• 240
• 245
• 250
• 235

Answer explanation

230 + 15 − 5 = 240.