Instances of Classes

java is object-oriented programming, java is about manipulating objects
objects are a reference type, when referring to it, you are referring to where it is stored
an object is an instance of a class

Constructors

to make object, call constructor, will initialize the object and make characteristics
Class object = new Class();

Constructor Overloading

one class can have multiple constructors, the different constructors need to have diff numbers of parameters or different order of variables, each constructor will make objects with same types of characteristics, but are created differently
parameters missing are given default parameters instead

Null Objects

object can be made null , makes it so no object exists for that

Void Methods vs. Non-Void Methods

void methods don't return value, change characteristics of object or prints text
static methods belong to a class, not tied to an object

static v non-static

dot notation to use static, classname.method()
non-static on a particular object, objectname.method()

write/call methods with parameters

parameters in the parentheses,
to call method, plug values in place of variables

Non-void method

use method as part of expression/stored as variable
dataType variableName = methodName(parameterListOptional);

Strings

string literals are objects
escape characters print a character or empty space
combine strings with concatenation, used through + operator

Vocab

Overloading a method, same name different parameters

When you use the same method name in a class each with different parameters.

Overriding a method, same signature of a method

When a subclass has the same name and parameters as the parent class

Late binding of object

Late binding is when the compiler runs the object and is created then and there

Polymorphism: any of overloading, overriding, late binding

Multiple methods with the same name but different parameters

Comparing Objects

import java.io.*;
 
class Pet {

    String name;
    int age;
    String breed;
 

    Pet(String name, int age, String breed)
    {
        this.name = name;
        this.age = age;
        this.breed = breed;
    }
}

public class Main {
 
    public static void main(String args[])
    {
 
        Pet dog1 = new Pet("Snow", 3, "German Shepherd"); //late binding
        Pet cat = new Pet("Jack", 2, "Tabby"); //overriding method different
        Pet dog2 = new Pet("Snow", 3, "German Shepherd"); //overriding method same
        
        
        System.out.println(dog1.equals(dog2));
    }
}

Main.main(null);

false

equals and hashCode methods can be used to compare objects
equals method compares equality of two objects

Standard methods: toString(), equals(), hashCode()

toString() method returns a string representation of a class
equals() compares two strings
hashCode() returns the integer value that is associated with all values in Java(aka the hash code)

Abstract Class, Abstract Method

This class’s objects and methods can be referenced, however the class itself is not initialized.

google form

FRQs

a)

public int scoreGuess( String guess )
{
    int val = 0;
    int len = guess.length();
    for( int i = 0; i <= secret.length()-len; i+=1)
    {
        String ck = secret.substring( i, i+len );
        if( ck.equals(guess) )
            val++;
    }
    return val*len*len;
}

b)

public String findBetterGuess(String guess1, String guess2 )
{
    int a = scoreGuess( guess1 );
    int b = scoreGuess( guess2 );
    if( a > b ) return guess1;
    if( b > a ) return guess2;
    if( guess1.compareTo( guess2 ) > 0 )
    return guess1;
    return guess2;
}