Java variable values not being passed to new class

You need to call createHero() on a CharBuilder before you call getHero() in your constructor.

Your code should be,

    List<Enemy> enemyList = new Enemy().createList();
    Enemy enemy = enemyList.get(randNum.nextInt(enemyList.size()));
    CharBuilder cb = new CharBuilder();
    cb.createHero();
    CharBuilder character = cb.getHero();
    int charStrength = character.getStrength();
    int charHp = character.getHP();
    int enemyHp = enemy.getHP();
    int enemyStr =enemy.getStr();
    String enemyName = enemy.getName();

The reason for this is because you need to execute createHero() in order to initialize the hero object.

Further go more on this, you are initializing CharBuilder inside CharBuilder which is not a good practice when we think in terms of object orientation. One alternative is to use the singleton pattern here.

Lets see why you have NPE issue:

Take a look at here

public CharBuilder() {

}

The first constructor is a default constructor. It only initializes the bare minimum and lets users set the rest with getters and setters.

CharBuilder character = new CharBuilder().getHero();
some setters is missing here?
int charStrength = character.getStrength();

As you see in your code, you did not set anything to get it after wards

In addition, There are three common reasons to define a default constructor:

1. To construct an object with default values.
2. To initialize an object that doesn't need parameters in that initialization process.
3. To redefine the scope of the constructor. Making the constructor private will prevent anyone but the class itself from constructing an object.

If you want to make sure that any instance created is always valid and any member variables are always initialized,then you would define the constructor which initializes all the required member variables.

In your case, you can use createHero function before getHero because createHero sets the values up.

Suggestion:

Plaese take a look at builder pattern for designing a better class

More Info About Builder Pattern

As has already been pointed out, you are not calling createHero, which generates the instance of CharBuilder which getHero returns. Thus returning a null value.

The problem seems to steam from a misunderstanding of what a builder should do. A builder should take raw material and build something, it shouldn't return a copy of it self.

For example...

public class CharBuilder {

    static public Random randNum = new Random();

    private String mCharacterName;
    private int mStrength = 6;
    private int mIntelligence = 6;
    private int mConstitution = 6;
    private int mDexterity = 6;
    private int mHitPoints = 40;
    private int mManaPoints = 40;
    private String mCharClass;
    private String classType;

    public Character createHero() {
        // Valid the properties you have been given...

        if ("warrior".equalsIgnoreCase(classType)) {
            mCharClass = "warrior";
            mStrength = mStrength + 3;
            mIntelligence = mIntelligence - 1;
            mConstitution = mConstitution + 4;
            mDexterity = mDexterity + 1;
            mHitPoints = mHitPoints + 20;
            mManaPoints = mManaPoints - 10;
        } else if ("Wizard".equalsIgnoreCase(classType)) {
            mCharClass = "wizard";
            mStrength = (mStrength - 1);
            mIntelligence = (mIntelligence + 3);
            mConstitution = (mConstitution + 2);
            mDexterity = (mDexterity);
            mHitPoints = (mHitPoints - 10);
            mManaPoints = (mManaPoints + 30);
        } else if ("thief".equalsIgnoreCase(classType) || "thievery".equalsIgnoreCase(classType)) {
            mCharClass = "thief";
            mStrength = (mStrength + 2);
            mIntelligence = (mIntelligence + 1);
            mConstitution = (mConstitution + 1);
            mDexterity = (mDexterity + 5);
            mHitPoints = (mHitPoints + 10);
            mManaPoints = (mManaPoints + 10);
        } else {
            throw new UnsupportedOperationException("Unknown class");
        }

        return new DefaultCharacter(mCharacterName, mStrength, mIntelligence, mConstitution, mDexterity, mHitPoints, mManaPoints, mCharClass);
    }

    public CharBuilder setCharacterName(String mCharacterName) {
        this.mCharacterName = mCharacterName;
        return this;
    }

    public CharBuilder setStrength(int mStrength) {
        this.mStrength = mStrength;
        return this;
    }

    public CharBuilder setIntelligence(int mIntelligence) {
        this.mIntelligence = mIntelligence;
        return this;
    }

    public CharBuilder setConstitution(int mConstitution) {
        this.mConstitution = mConstitution;
        return this;
    }

    public CharBuilder setDexterity(int mDexterity) {
        this.mDexterity = mDexterity;
        return this;
    }

    public CharBuilder setHitPoints(int mHitPoints) {
        this.mHitPoints = mHitPoints;
        return this;
    }

    public CharBuilder setManaPoints(int mManaPoints) {
        this.mManaPoints = mManaPoints;
        return this;
    }

    public CharBuilder setCharClass(String mCharClass) {
        this.mCharClass = mCharClass;
        return this;
    }

    public CharBuilder setClassType(String classType) {
        this.classType = classType;
        return this;
    }

}

You can use method chaining to make it easier to call, for example

Character character = new CharBuilder().
                setCharClass("Wizard").
                setCharacterName("Bob").
                setConstitution(10).
                setDexterity(10).
                setHitPoints(10).
                setIntelligence(10).
                setManaPoints(10).
                setStrength(10).
                createHero();

The builder shouldn't be asking questions of the user, this information should already have been obtained and simply given to the builder. You should only call the methods which you need in order to build character, so many of the methods in the above example might be omitted in favor of default values

Character character = new CharBuilder().
                setCharClass("Wizard").
                setCharacterName("Bob").
                createHero();

The builder should validate the properties it has been given and throw an Exception if one or required properties are missing (like the name or class)

I, personally, like to work with interfaces, rather then implementations, it allows you to define the public contract that a object can have, for example...

public interface Character {
    public String getCharacterName();
    public int getStrength();
    public int getIntelligence();
    public int getConstitution();
    public int getDexterity();
    public int getHitPoints();
    public int getanaPoints();
    public String getCharClass();
}

Which can be wrapped in

public class DefaultCharacter implements Character {

    private final String mCharacterName;
    private final int mStrength;
    private final int mIntelligence;
    private final int mConstitution;
    private final int mDexterity;
    private final int mHitPoints;
    private final int mManaPoints;
    private final String mCharClass;

    public Character(String mCharacterName, int mStrength, int mIntelligence, int mConstitution, int mDexterity, int mHitPoints, int mManaPoints, String mCharClass) {
        this.mCharacterName = mCharacterName;
        this.mStrength = mStrength;
        this.mIntelligence = mIntelligence;
        this.mConstitution = mConstitution;
        this.mDexterity = mDexterity;
        this.mHitPoints = mHitPoints;
        this.mManaPoints = mManaPoints;
        this.mCharClass = mCharClass;
    }

    public String getCharacterName() {
        return mCharacterName;
    }

    public int getStrength() {
        return mStrength;
    }

    public int getIntelligence() {
        return mIntelligence;
    }

    public int getConstitution() {
        return mConstitution;
    }

    public int getDexterity() {
        return mDexterity;
    }

    public int getHitPoints() {
        return mHitPoints;
    }

    public int getManaPoints() {
        return mManaPoints;
    }

    public String getCharClass() {
        return mCharClass;
    }

}

Now, because the CharBuilder only says it will return a Character, you can change the physical implementation anyway you like

In this way, it's pretty hard to run into the problem you are having, because either the builder is going to return a valid Character or throw an Exception

Take a closer look at the Builder Pattern for more details