Basics – Page 3 – Program Creek

Yet Another “Java Passes By Reference or By Value”?

December 26, 2013August 13, 2011 by ProgramCreek

This is a classic interview question which confuses novice Java developers. In this post I will use an example and some diagram to demonstrate that: Java is pass-by-value. 1. Some Definitions Pass by value: make a copy in memory of the actual parameter’s value that is passed in. Pass by reference: pass a copy of … Read more

How to Build Your Own Java library?

December 29, 2013July 4, 2011 by ProgramCreek

Code reuse is one of the most important factors in software development. It is a VERY good idea to put frequently-used functions together and build a library for yourself. Whenever some method is used, just simply make a method invocation. For Java, it’s straightforward to manage such a library. Here a simple example in Eclipse. The library will contain only one “add” method for demo purpose.

Step 1: Create a “Java Project” named as “MyMath”, and a simple “add” method under “Simple” class.

Package structure is as follows:

Check a character in a String is number or not in Java

October 14, 2013April 11, 2011 by ProgramCreek

All you need is this simple function in java.lang package. Character.isDigit(c)Character.isDigit(c) Of course, if want to check a character in a string, need to get the char first by using the following. str.charAt(i)str.charAt(i)

A method to detect if string contains only uppercase letter in Java

October 6, 2013April 11, 2011 by ProgramCreek

My approach This method loop through each character in the string, and determine if each character is in upper case. Upper case letter value is from 97 to 122. public static boolean testAllUpperCase(String str){ for(int i=0; i<str.length(); i++){ char c = str.charAt(i); if(c >= 97 && c <= 122) { return false; } } //str.charAt(index) … Read more

Declaration, Initialization and Scoping for Java

October 8, 2012March 1, 2009 by ProgramCreek

The following is a summary for showing Java declaration, initialization and scoping. Variables defined in try block are not visible in catch block. You cannot pass parameters when you implement an interface by an anonymous class. Constructors cannot return anything. Not even void. Every enum has a values() method that returns an array of all … Read more

Overriding vs. Overloading in Java

January 23, 2016February 26, 2009 by ProgramCreek

Overriding and Overloading are two very important concepts in Java. They are confusing for Java novice programmers. This post illustrates their differences by using two simple examples. 1. Definitions Overloading occurs when two or more methods in one class have the same method name but different parameters. Overriding means having two methods with the same … Read more

Simple example to show how to use Date Formatting in Java

December 25, 2013February 16, 2009 by ProgramCreek

Simple example to show how to use Date Formatting in Java

Diagram to show Java String’s Immutability

October 6, 2020February 10, 2009 by ProgramCreek

Here are a set of diagrams to illustrate Java String’s immutability. 1. Declare a string The following code initializes a string s. String s = "abcd";String s = "abcd"; The variable s stores the reference of a string object as shown below. The arrow can be interpreted as “store reference of”. 2. Assign one string … Read more