Code showing alternative to the standard Builder pattern implementation in Java. Also see blogpost at http://branchandbound.net/blog/java/2013/10/failed-experiment-improving-builder-pattern/

PizzaOrder.java

package net.branchandbound.builder;

import java.util.concurrent.atomic.AtomicBoolean;

public class PizzaOrder {

    private int size;
    private boolean pepperoni;
    private boolean chicken;
    private boolean mushroom;
    private boolean peppers;
    private String cheese;
    private String sauce;
    private String orderFor;
    
    private PizzaOrder() {
        // Prevent direct instantiation
    }
    
    public static Builder pizzaOrder(int size, String sauce, String orderFor) {
        return new PizzaOrder().new Builder(size, sauce, orderFor);
    }
    
    public class Builder {
        private AtomicBoolean build = new AtomicBoolean(false);

        public Builder(int _size, String _sauce, String _orderFor) {
            size = _size;
            sauce = _sauce;
            orderFor = _orderFor;
        }

        public Builder withPepperoni() {
            throwIfBuild();
            pepperoni = true;
            return this;
        }

        public Builder withChicken() {
            throwIfBuild();
            chicken = true;
            return this;
        }

        public Builder withMushroom() {
            throwIfBuild();
            mushroom = true;
            return this;
        }

        public Builder withPeppers() {
            throwIfBuild();
            peppers = true;
            return this;
        }

        public Builder withCheese(String _cheese) {
            throwIfBuild();
            cheese = _cheese;
            return this;
        }
        
        public PizzaOrder build() {
            if (build.compareAndSet(false, true)) {
                // check consistency here...                
                return PizzaOrder.this;
            } else {
                throw new IllegalStateException("Build may only be called once!");
            }
        }
        private void throwIfBuild() {
            if (build.get()) {
                throw new IllegalStateException("Cannot modify builder after calling build()");
            }
        }
    }

    public int getSize() {
        return size;
    }

    public boolean isPepperoni() {
        return pepperoni;
    }

    public boolean isChicken() {
        return chicken;
    }

    public boolean isMushroom() {
        return mushroom;
    }

    public boolean isPeppers() {
        return peppers;
    }

    public String getCheese() {
        return cheese;
    }

    public String getSauce() {
        return sauce;
    }

    public String getOrderFor() {
        return orderFor;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((cheese == null) ? 0 : cheese.hashCode());
        result = prime * result + (chicken ? 1231 : 1237);
        result = prime * result + (mushroom ? 1231 : 1237);
        result = prime * result + ((orderFor == null) ? 0 : orderFor.hashCode());
        result = prime * result + (pepperoni ? 1231 : 1237);
        result = prime * result + (peppers ? 1231 : 1237);
        result = prime * result + ((sauce == null) ? 0 : sauce.hashCode());
        result = prime * result + size;
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        PizzaOrder other = (PizzaOrder) obj;
        if (cheese == null) {
            if (other.cheese != null)
                return false;
        } else if (!cheese.equals(other.cheese))
            return false;
        if (chicken != other.chicken)
            return false;
        if (mushroom != other.mushroom)
            return false;
        if (orderFor == null) {
            if (other.orderFor != null)
                return false;
        } else if (!orderFor.equals(other.orderFor))
            return false;
        if (pepperoni != other.pepperoni)
            return false;
        if (peppers != other.peppers)
            return false;
        if (sauce == null) {
            if (other.sauce != null)
                return false;
        } else if (!sauce.equals(other.sauce))
            return false;
        if (size != other.size)
            return false;
        return true;
    }
    
}

PizzaOrderOldStyle.java

package net.branchandbound.builder;


public class PizzaOrderOldStyle {

    private int size;
    private boolean pepperoni;
    private boolean chicken;
    private boolean mushroom;
    private boolean peppers;
    private String cheese;
    private String sauce;
    private String orderFor;

    public static Builder pizzaOrder(int size, String sauce, String orderFor) {
        return new PizzaOrderOldStyle.Builder(size, sauce, orderFor);
    } 
    
    public static class Builder {
        
        private int size;
        private boolean pepperoni;
        private boolean chicken;
        private boolean mushroom;
        private boolean peppers;
        String cheese;
        private String sauce;
        private String orderFor;

        public Builder(int size, String sauce, String orderFor) {
            this.size = size;
            this.sauce = sauce;
            this.orderFor = orderFor;
        }

        public Builder withPepperoni() {
            this.pepperoni = true;
            return this;
        }

        public Builder withChicken() {
            this.chicken = true;
            return this;
        }

        public Builder withMushroom() {
            this.mushroom = true;
            return this;
        }

        public Builder withPeppers() {
            this.peppers = true;
            return this;
        }

        public Builder withCheese(String cheese) {
            this.cheese = cheese;
            return this;
        }

        public PizzaOrderOldStyle build() {
            // check consistency here...
            return new PizzaOrderOldStyle(this);
        }
    }

    private PizzaOrderOldStyle(Builder builder) {
        size = builder.size;
        pepperoni = builder.pepperoni;
        chicken = builder.chicken;
        mushroom = builder.mushroom;
        peppers = builder.peppers;
        cheese = builder.cheese;
        sauce = builder.sauce;
        orderFor = builder.orderFor;
    }

    public int getSize() {
        return size;
    }

    public boolean isPepperoni() {
        return pepperoni;
    }

    public boolean isChicken() {
        return chicken;
    }

    public boolean isMushroom() {
        return mushroom;
    }

    public boolean isPeppers() {
        return peppers;
    }

    public String getCheese() {
        return cheese;
    }

    public String getSauce() {
        return sauce;
    }

    public String getOrderFor() {
        return orderFor;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((cheese == null) ? 0 : cheese.hashCode());
        result = prime * result + (chicken ? 1231 : 1237);
        result = prime * result + (mushroom ? 1231 : 1237);
        result = prime * result + ((orderFor == null) ? 0 : orderFor.hashCode());
        result = prime * result + (pepperoni ? 1231 : 1237);
        result = prime * result + (peppers ? 1231 : 1237);
        result = prime * result + ((sauce == null) ? 0 : sauce.hashCode());
        result = prime * result + size;
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        PizzaOrderOldStyle other = (PizzaOrderOldStyle) obj;
        if (cheese == null) {
            if (other.cheese != null)
                return false;
        } else if (!cheese.equals(other.cheese))
            return false;
        if (chicken != other.chicken)
            return false;
        if (mushroom != other.mushroom)
            return false;
        if (orderFor == null) {
            if (other.orderFor != null)
                return false;
        } else if (!orderFor.equals(other.orderFor))
            return false;
        if (pepperoni != other.pepperoni)
            return false;
        if (peppers != other.peppers)
            return false;
        if (sauce == null) {
            if (other.sauce != null)
                return false;
        } else if (!sauce.equals(other.sauce))
            return false;
        if (size != other.size)
            return false;
        return true;
    }

}

PizzaOrderOldStyleTest.java

package net.branchandbound.builder.test;

import static net.branchandbound.builder.PizzaOrderOldStyle.pizzaOrder;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
import net.branchandbound.builder.PizzaOrderOldStyle;
import net.branchandbound.builder.PizzaOrderOldStyle.Builder;

import org.junit.Test;

public class PizzaOrderOldStyleTest {

    @Test
    public void valuesShouldBeRetained() {
        PizzaOrderOldStyle pizzaOrder =
            pizzaOrder(10, "tomato", "Sander")
                .withPepperoni()
                .withMushroom()
                .withCheese("parmesan").build();

        assertEquals(10, pizzaOrder.getSize());
        assertEquals("tomato", pizzaOrder.getSauce());
        assertEquals("Sander", pizzaOrder.getOrderFor());
        assertTrue(pizzaOrder.isPepperoni());
        assertFalse(pizzaOrder.isChicken());
        assertTrue(pizzaOrder.isMushroom());
        assertFalse(pizzaOrder.isPeppers());
        assertEquals("parmesan", pizzaOrder.getCheese());
    }

    @Test
    public void testEqualsHashCode() {
        Builder builder = pizzaOrder(10, "tomato", "Sander").withPepperoni().withMushroom().withCheese("parmesan");
        PizzaOrderOldStyle a = builder.build();
        PizzaOrderOldStyle b = builder.build();
        assertEquals(a, b);
        assertEquals(a.hashCode(), b.hashCode());
    }
}

PizzaOrderTest.java

package net.branchandbound.builder.test;

import static net.branchandbound.builder.PizzaOrder.pizzaOrder;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
import net.branchandbound.builder.PizzaOrder;
import net.branchandbound.builder.PizzaOrder.Builder;

import org.junit.Test;

public class PizzaOrderTest {
    
    @Test
    public void valuesShouldBeRetained() {
        PizzaOrder pizzaOrder =
            pizzaOrder(10, "tomato", "Sander").withPepperoni().withMushroom()
                .withCheese("parmesan").build();
        
        assertEquals(10, pizzaOrder.getSize());
        assertEquals("tomato", pizzaOrder.getSauce());
        assertEquals("Sander", pizzaOrder.getOrderFor());
        assertTrue(pizzaOrder.isPepperoni());
        assertFalse(pizzaOrder.isChicken());
        assertTrue(pizzaOrder.isMushroom());
        assertFalse(pizzaOrder.isPeppers());
        assertEquals("parmesan", pizzaOrder.getCheese());
    }
    
    @Test
    public void testEqualsHashCode() {
        PizzaOrder a = getCorrectlyFilledBuilder().build();
        PizzaOrder b = getCorrectlyFilledBuilder().build();
        assertEquals(a, b);
        assertEquals(a.hashCode(), b.hashCode());
    }

    @Test(expected = IllegalStateException.class)
    public void cannotBuildTwice() {
        Builder builder = getCorrectlyFilledBuilder();
        builder.build();
        builder.build();
    }
    
    @Test(expected = IllegalStateException.class)
    public void cannotUseBuilderAfterBuild() {
        Builder correctlyFilledBuilder = getCorrectlyFilledBuilder();
        correctlyFilledBuilder.build();
        correctlyFilledBuilder.withCheese("FAIL");
    }
    
    private Builder getCorrectlyFilledBuilder() {
        return pizzaOrder(10, "tomato", "Sander").withPepperoni().withMushroom()
                        .withCheese("parmesan");
    }

    
}