Types
Objects
Strings
Miscellaneous

100

What is a boolean?

A primitive data type that can either be true or false.

100

What does a constructor do?

It creates an object and initializes all the instance variables. 

100

What does the following return: 

"hello".length();

5. This is because length() returns the number of characters a String has. 

100

What are 3 different ways to increment this by one: 

int x = 7;

x = x + 1;

x++;

++x;

x += 1;

200

int x = 4; 

String str = "hi" 

What is the type of x + str?

String

200

What types of constructors are these?

public class Dragon {

   //Data members

   public Dragon () {

     //...

   }

   public Dragon (Dragon other) {

     //...

   }

}

Default and copy constructors

200

What does this return: 

"watermelon".substring(4, 8);

rmel

200

What is overloading?

A feature that allows a class to have more than one method having the same name, if their argument lists are different.

300

int x = 5;

int y = 2;

int z = x/y;

2

300

What is the purpose of the equals method? 

To compare Objects based on their instance/field variables, rather than by their place in memory.

300

What does this return:
"Hello".equals("hello")

false

300

What is the difference between a primitive and an Object?

Objects have field variables, their own methods, have to be "constructed", and can contain multiple pieces of information. Often, they represent something in real life. These can either be written by you or are given by Java.

400

What does this print out?

int x = 5;

double y = 2.0;

System.out.println(x/y);

2.5

400

What does the keyword "this" refer to?

The keyword "this" refers to the current object that you are writing code for. For example, you can refer to the current object's instance variables as: this.fieldName. This is used often in the constructor and the object's methods.

400

What does this return: 

"strawberry".indexOf("r");

"start".indexOf("c");

"household".indexOf("hold");

2

-1

5

400

What does this do:

int s = 0;

int total = 0;

while (s < 25) { 

      if (s % 5 == 0) { 

          total = total + s;

      }

      s++;

}

It adds up all the multiples of 5 starting at 0 and going up to (but not including) 25. 

500

What is a Wrapper class? 

ex. Integer for int

It is a class whose object contains/wraps primitive data types. It has methods you can use for primitive data types. You can think of it like an Object version of a primitive data type.

500

Say we wrote a class Laptop without an equals method. What does the following print out?

Laptop x = new Laptop();

Laptop y = new Laptop(x);

Laptop z = x; 

System.out.println(x.equals(y));

System.out.println(x.equals(z));

false

true

500

What do these return (positive/negative/zero): 

"apricot".compareTo("banana");

"tree".compareTo("TREE".toLowerCase());

"cat".compareTo("apricot".substring(4));

negative

zero

negative

500

What is wrong with this code: 

int i = 4;

int j = 5;

while (i % j <= 5) {

   if (j % 5 == 2) { 

       j += 6;

   }

   j++;

}

The loop will infinitely run since i is never incremented, so i % j will always be less than or equal to 5.