Generic types are extensively used in Java collections. Why do we need Generic types in Java? Understanding this question can help us better understand a lot of related concepts. In this article, I will use a very short example to illustrate why Generic is useful. 1. Overview of Generics The goal of implementing Generics is … Read more
This post shows how to setup a python web development environment under Ubuntu and make a hello world example. So Python has become a hot word in recent years. But before you can do anything about it, you need a “hello world” sample application. In this post, I will build a hello world Python web … Read more
Github is a more popular and social code repository. It is the trend to be a user, at least it is true for now. There are a lot of problems we may meet, most of them can be solved by reading the documentation. But that is not fast or something we like to do. Problem … Read more
You may wonder what a Java class looks like as an Abstract Syntax Tree(AST). We can view AST of any Java class by using Eclipse ASTView. The AST can be easily showed in a separate view under eclipse IDE. For the following simple java class, the ASTView shows the complete AST. public class Test { … Read more
Given two strings A and B, find the minimum number of times A has to be repeated such that B is a substring of it. If no such solution, return -1. For example, with A = “abcd” and B = “cdabcdab”. Return 3, because by repeating A three times (“abcdabcdabcdâ€), B is a substring of … Read more
There are N workers. The i-th worker has a quality[i] and a minimum wage expectation wage[i]. Now we want to hire exactly K workers to form a paid group. When hiring a group of K workers, we must pay them according to the following rules: Every worker in the paid group should be paid in … Read more
Given two strings s1 and s2, write a function to return true if s2 contains the permutation of s1. In other words, one of the first string’s permutations is the substring of the second string. For example: Input: s1 = “ab” s2 = “eidbaooo” Output: True Explanation: s2 contains one permutation of s1 (“ba”). Java … Read more
Given a string of math expression, such as 1-(2+3), evaluate the value. The expression contains only digits, +, – and parentheses. Java Solution import java.util.ArrayList; import java.util.Stack; public class ExpressionEvaluator { static class Node { Boolean isPositive; Integer value; ArrayList<Node> list; public Node(boolean isPositive, Integer value) { this.isPositive = isPositive; this.value = value; … Read more
Given two strings S and T, return if they are equal when both are typed into empty text editors. # means a backspace character. Example 1: Input: S = “ab#c”, T = “ad#c” Output: true Explanation: Both S and T become “ac”. Example 2: Input: S = “a##c”, T = “#a#c” Output: true Explanation: Both … Read more
If you develop an RCP rich client application, sooner or later you will have to know some layout to organize the widgets in your view. This code example requires that you have an RCP application with a view. Here is how to make an RCP app with a view. This tutorial is about the most … Read more
This article contains JUnit annotations and examples for showing how to use them. Annotations enables us to use any method names without following any conventions. Actually, it has becomes a very popular way for a lot of projects, framework, etc. You may ask questions like: How to skip a test case in Junit? How to … Read more
If we want to calculate square root, we can use Math.sqrt() method. It is simple. Now do you know how to write such a method by yourself? Here is the equation you need. The first sqrt number should be the input number / 2. Using the equation, we can come up with a Java Square … Read more
Introduction and Installation JUnit is the defacto standard for unit testing. JUnit is part of Eclipse Java Development Tools (JDT). So, we can either install JDT via Software Updates site, or download and install Eclipse IDE for Java Developers. Using JUnit in Eclipse Environment 1. Create a project and create a class. This should contains the method you want … Read more
Why do we need to test our program? When people talk about the importance of software testing, common examples they give frequently are military software, aircraft, etc. That is not concrete enough to understand why we need to test our software. Here I provide an example from daily programming work. You don’t need to work … Read more
How to shuffle an array in Java? There are two approaches to shuffle an int array(randomizes the order of the elements in an array), one is to use the Collections.shuffle() method, the other is to manipulate array elements. Approach 1: Shuffle elements in an array This is flexible, and easy to be changed to fit … Read more