Java for beginners!: Tips and Tricks

TIPS & TRICKS FOR JAVA DEVELOPER

1: Avoid creating unnecessary objects and always prefer to do Lazy Initialization

Object creation in Java is one of the most expensive operation in terms of memory utilization and performance impact. It is thus advisable to create or initialize an object only when it is required in the code.

public class Countries {

    private List countries;

    public List getCountries() {

        //initialize only when required

        if(null == countries) {

            countries = new ArrayList();

        }

        return countries;

    }

}

2: Never make an instance fields of class public

Making a class field public can cause lot of issues in a program. For instance you may have a class called MyCalender. This class contains an array of String weekdays. You may have assume that this array will always contain 7 names of weekdays. But as this array is public, it may be accessed by anyone. Someone by mistake also may change the value and insert a bug!

public class MyCalender {

    public String[] weekdays =

        {"Sun", "Mon", "Tue", "Thu", "Fri", "Sat", "Sun"};

    //some code 

}

Best approach as many of you already know is to always make the field private and add a getter method to access the elements.

1

2

3

4

5

6

private String[] weekdays =

    {"Sun", "Mon", "Tue", "Thu", "Fri", "Sat", "Sun"};

public String[] getWeekdays() {

    return weekdays;

}

But writing getter method does not exactly solve our problem. The array is still accessible. Best way to make it unmodifiable is to return a clone of array instead of array itself. Thus the getter method will be changed to.

public String[] getWeekdays() {

    return weekdays.clone();

}

3: Always try to minimize Mutability of a class

Making a class immutable is to make it unmodifiable. The information the class preserve will stay as it is through out the lifetime of the class. Immutable classes are simple, they are easy to manage. They are thread safe. They makes great building blocks for other objects.

However creating immutable objects can hit performance of an app. So always choose wisely if you want your class to be immutable or not. Always try to make a small class with less fields immutable.

To make a class immutable you can define its all constructors private and then create a public static method
to initialize and object and return it.

public class Employee {

    private String firstName;

    private String lastName;

    //private default constructor

    private Employee(String firstName, String lastName) {

        this.firstName = firstName;

        this.lastName = lastName;

    }

    public static Employee valueOf (String firstName, String lastName)

   {

        return new Employee(firstName, lastName);

    }

}

4: Try to prefer Interfaces instead of Abstract classes

First you can not inherit multiple classes in Java but you can definitely implements multiple interfaces. Its very easy to change the implementation of an existing class and add implementation of one more interface rather then changing full hierarchy of class.

5: Always try to limit the scope of Local variable

Local variables are great. But sometimes we may insert some bugs due to copy paste of old code. Minimizing the scope of a local variable makes code more readable, less error prone and also improves the maintainability of the code.

Always initialize a local variable upon its declaration. If not possible at least make the local instance assigned null value.

6: Try to use standard library instead of writing your own from scratch

Writing code is fun. But “do not reinvent the wheel”. It is very advisable to use an existing standard library which is already tested, debugged and used by others. This not only improves the efficiency of programmer but also reduces chances of adding new bugs in your code. Also using a standard library makes code readable and maintainable.

For instance Google has just released a new library Google Collections that can be used if you want to add advance collection functionality in your code.

7: Wherever possible try to use Primitive types instead of Wrapper classes

Wrapper classes are great. But at same time they are slow. Primitive types are just values, whereas Wrapper classes are stores information about complete class.

Sometimes a programmer may add bug in the code by using wrapper due to oversight. For example, in below example:

int x = 10;

int y = 10;

Integer x1 = new Integer(10);

Integer y1 = new Integer(10);

System.out.println(x == y);

System.out.println(x1 == y1);

The first sop will print true whereas the second one will print false. The problem is when comparing two wrapper class objects we cant use == operator. It will compare the reference of object and not its actual value.

Also if you are using a wrapper class object then never forget to initialize it to a default value. As by default all wrapper class objects are initialized to null.

Boolean flag;

if(flag == true) {

    System.out.println("Flag is set");

} else {

    System.out.println("Flag is not set");

}

The above code will give a NullPointerException as it tries to box the values before comparing with true and as its null.

8: Use Strings with utmost care.

Always carefully use Strings in your code. A simple concatenation of strings can reduce performance of program. For example if we concatenate strings using + operator in a for loop then everytime + is used, it creates a new String object. This will affect both memory usage and performance time.

Also whenever you want to instantiate a String object, never use its constructor but always instantiate it directly. For example:

//slow instantiation

String slow = new String("Yet another string object");

//fast instantiation

String fast = "Yet another string object";