minte9

learningjourney

Static Factory

 
/**
 * Static factory methods return an instance of a class.
 * 
 * One advantage is that, unlike constructors, they have names.
 * The resulting code is easier to read.
 * 
 * Second, you don't need to create an object every time.
 */

package com.minte9.effective.constructors;

public class StaticFactory {
    public static void main(String[] args) {

        MyClass.getInstance();
            // Class constructor

        MyClass.getInstance();
            // nothing
    }
}

class MyClass {

    private static final MyClass INSTANCE = new MyClass();

    public static MyClass getInstance() { // Look Here
        return INSTANCE; 
    }

    private MyClass() {
        System.out.println("Class constructor");
    }
}

Telescoping

 
/**
 * Telescoping constructors works, but ...
 * it is hard to write and hard to read.
 */

package com.minte9.effective.constructors;

public class Telescoping {

    public static void main(String[] args) {

        new Nutrition(240);
        new Nutrition(240, 100);
        new Nutrition(240, 100, 10);

        /*
            Constructor (size, calories, fat) 240 0 0
            Constructor (size, calories, fat) 240 100 0
            Constructor (size, calories, fat) 240 100 10
        */
    }
}

class Nutrition {

    public Nutrition(int size) { // one param always required
        this(size, 0);
    }

    public Nutrition(int size, int calories) {
        this(size, calories, 0);
    }

    public Nutrition(int size, int calories, int fat) {
        System.out.println(
            "Constructor (size, calories, fat) "
            + size + " " 
            + calories + " "
            + fat
        );
    }
}

JavaBeans

 
/**
 * A JavaBeans constructor object ...
 * may be in an inconsistent state
 */

package com.minte9.effective.constructors;

public class Javabeans {
    public static void main(String[] args) {

        A a = new A();

        a.setSize(240);
            // setSize: 240

        a.setCalories(100);
            // setCalories: 100

        a.setFat(11);
            // setFat: 11
    }
}

class A {

    private int size = -1; // required, no default
    private int calories = 0;
    private int fat = 0;
    
    public void setSize(int s) { 
        size = s; 
        System.out.println("setSize: " + size);
    }

    public void setCalories(int s) { 
        calories = s; 
        System.out.println("setCalories: " + calories);
    }

    public void setFat(int s) { 
        fat = s; 
        System.out.println("setFat: " + fat);
    }
}

Builder

 
/**
 * Consider a builder when faced with many constructor parameters
 */

package com.minte9.effective.constructors;

public class BuilderApp {
    public static void main(String[] args) {

        N n = new N.Builder(240)
            .calories(100)
            .fat(11)
            .build(); 

        System.out.println(n.getFat()); 
            // 11
    }
}

class N {

    private final int size;
    private final int calories;
    private final int fat;

    public static class Builder {

        private int size;
        private int calories = 0;
        private int fat = 0;
        
        public Builder(int s) {
            size = s; 
        }

        public Builder calories(int c) { 
            calories = c; 
            return this; 
        }

        public Builder fat(int f) { 
            fat = f; 
            return this; 
        }

        public N build() { 
            return new N(this); 
        }
    }
    
    private N(Builder builder) {
        size = builder.size;
        calories = builder.calories;
        fat = builder.fat;
    }

    public int getSize() { 
        return size; 
    }

    public int getCalories() { 
        return calories; 
    }

    public int getFat() { 
        return fat; 
    }
}