Correct and incorrect implementation of a subclass of bread. Note this isn't compilable due to having 3 public classes in the same file, if you separate them into separate files they should compile.

Bread.java

// base class
public class Bread {
  private String name;
  private int amount;
  
  public Bread(String name, int amount) {
    this.name = name;
    this.amount = amount;
  }
  
  public int getAmount() {
    return this.amount;
  }
}

// incorrect
public class BrownBread extends Bread {
  private String name;
  private int amount;
  
  protected static final double PRICE_PER_ITEM = 1.1;
  
  public BrownBread(String name, int amount) {
    // note that this.name and this.amount are never set by this constructor and thus have the values null and 0 respectively
    super(name, amount);
  }
  
  public double calculateTypePrice() {
    // this.amount will always be 0 since it is not set in the constructor
    return this.amount * PRICE_PER_ITEM;
  }
}

// correct
public class BrownBread extends Bread {
  protected static final double PRICE_PER_ITEM = 1.1;
  
  public BrownBread(String name, int amount) {
    // this line is now correct because we will use the super class Bread's properties via getters and setters
    super(name, amount);
  }
  
  public double calculateTypePrice() {
    // super.getAmount() will call Bread's getAmount which is set in the constructor this time
    // also note that this.getAmount() is equivalent to super.getAmount() since it is inhereted from Bread
    // however in this case I like to use super because I find it more explicit where the method is originating from.
    return super.getAmount() * PRICE_PER_ITEM;
  }
}

// another possibility if you don't want to use getters/setters in a subclass
public class Bread {
  // protected values are available in subclasses
  protected String name;
  protected int amount;
  
  public Bread(String name, int amount) {
    this.name = name;
    this.amount = amount;
  }
}

public class BrownBread extends Bread {
  protected static final double PRICE_PER_ITEM = 1.1;
  
  public BrownBread(String name, int amount) {
    super(name, amount);
  }
  
  public double calculateTypePrice() {
    return amount * PRICE_PER_ITEM;
  }
}