java code snippets for practice

), and new HashMap (256) if it can be estimated to have 2000 elements.10. When copying large amounts of data, use the system.arraycopy () command11. Multiplication and division using shift operationsFor example:for (val = 0; Val The shift operation can greatly improve performance, because at the bottom of the computer, the bitwise operation is the most convenient and fastest, so it is recommended to modify:for (val = 0; Val Although the shift operation is fast, it may make the

between constants and variable 22, do not create some unused objects, do not import some unused classes It doesn't make sense if the code appears in the rdquo; The value of the local variable I am not usedrdquo;, rdquo; The import java.util is never usedrdquo, then remove these useless content 23, avoid using reflection during program Operation about, see reflection. Reflection is Java to provide users wit

want to store multiple mapping relationships in a HashMap instance, We need to set a large enough initialization size to store the mapping relationship more efficiently instead of letting the hash table grow automatically so that it rehash, causing performance bottlenecks. "In the practice of LinkedIn, it often comes across the need to traverse aArrayListand save these elements to theHashMapGo inside. Put thisHashMapInitializing the expected size avo

PrefaceCode optimization, a very important topic. Some people may feel useless, some small places have what good change, change and do not change the efficiency of the operation of the code has any impact? That's the question I'm thinking about, like a whale in the sea, is it useful to eat a little shrimp? No, but after eating a little shrimp, the whale is fed. Code optimization is also the same, if the pro

1) There is also a static block of code in Java in the form of static {...}. The static code block is part of the class definition and is called only once when the class is first loaded, and then the call is no longer loaded. So when did the class first get loaded? is in the main class (the class containing the main function) new an object instance (the class con

JUnit Unit Test Tutorial-The ultimate guide The ultimate guide to JUnit Unit Testing tutorials Description Introduction to Unit Testing 1 What is unit testing 2 Test coverage 3 unit tests in Java About JUnit 1 using Eclipse to implement a simple JUnit test example Implementing the complete JUnit example with eclipse 1 Creating a Project

The goals of code optimization are:1, reduce the volume of the Code2, improve the efficiency of code operationCode optimization details 1, specifying the final modifier of the class and method as much as possibleA class with a final modifier is not derived. In the Java Core API, there are many examples of final applications, such as Java.lang.String, where the en

Java 8? First, the Library is likely to discard the adapter class, and the default method is used to provide this function. Finally, the interface is in the following format: interfaceSimpleInput{ voidfoo(); defaultvoidbar(){ //somedefaultbehavior } } With this new interface, you can update the code and use the default method to replace the original adapter class. The best result of using

idea: those who write the framework is very good, when I can write a framework of their own? Sometimes look at other people's framework code, and feel very complicated, I have some suggestions on this and the new students need to learn what basis? Share some good ways.Abstract Ability: Abstraction of business and technology. Business abstraction is the ability to create the perfect entity classes and their connections after analyzing the requirements

programs, but a professional programmer. Can this book be used as an entry-level book? As a matter of fact, it is not difficult to get started with Java, just because its huge block header and relatively difficult content will make most beginners give up halfway. If you have no programming skills at all, of course you should not start with this. This is absolutely self-abuse. How to quickly learn this book? Let's take a look at

ObjectiveCode optimization, a very important topic. Some people may feel useless, some small places have what good change, change and do not change the efficiency of the operation of the code has any impact? That's the question I'm thinking about, like a whale in the sea, is it useful to eat a little shrimp? No, but after eating a little shrimp, the whale is fed. Code optimization is also the same, if the p

Building maintainable Software-java Write short Units of CodeAny fool can write code that a computer can understand. Good programmers WriteCode that humans can understand.-martin Fowlerguideline:? Limit The length of code units to lines of code.? Do the writing units that is longer than lines ofCode in the first place,

Building maintainable Software-java Write clean CodeWriting Clean code is the what you must does in order to call yourself a professional. -robert C. Martinguideline:? Write Clean Code.? Do the leaving code smells behind after developmentwork.? This improves maintainability because clean

the university to see a senior use this skill, then silently remember, and did not think much of what is going on. Notice these two days, originally is similar Java code template of an east. In a wonder why don't you define your own Android's Lenovo Word ...Step one: Open preference, search editor, select Java Editor, this time to find Sysout can see its definit

. out. println ("minx =" + minx + ", miniy =" + miny + ".");For (int I = minx; I For (int j = miny; j Int pixel = bi. getRGB (I, j); // The following three lines of code convert a number to an RGB number.Rgb [0] = (pixel 0xff0000)> 16;Rgb [1] = (pixel 0xff00)> 8;Rgb [2] = (pixel 0xff );System. out. println ("I =" + I + ", j =" + j + ":(" + rgb [0] + "," + rgb [1] + ", "+ rgb [2] + ")");}}}/*** Return the screen color value.** @ Param x* @ Param y*

The above combs through the annotations to complete the component scanning and automatic assembly, below to learn how to use the explicit configuration of the assembly beanSecond, assemble the Bean through Java classThe Helloworldconfig class is defined earlier, and using the @componentscan and @configuration annotations, @Configuration annotations indicate that the class is a Java configuration class that

top tip 60: Performance considerations, arrays are preferredArrays in the actual system development in the use of less, we usually only read some open source projects to see their figure, in Java it does not have list, set, map these collection classes are convenient, but in the basic type processing, the array is still dominant, And the bottom of the collection class is also implemented by arrays, such as summing a dataset:1//array sum 2 public

In the Web development process, especially in the background management system development, without adding and deleting the basic operation, the original my own practice is a copy of the paste, and then modify the differences, but this is both dull and wasted a lot of time, So according to the characteristics of their own project structure to write a tool jar automatically generated structure code, you can

The above combs through the annotations to complete the component scanning and automatic assembly, below to learn how to use the explicit configuration of the assembly beanSecond, assemble the Bean through Java classThe Helloworldconfig class is defined earlier, and using the @componentscan and @configuration annotations, @Configuration annotations indicate that the class is a Java configuration class that

type of error, which saves you the night to see the Halo tournament in the long run. Code Analysis As you can attest, the best feature of any good annotation or metadata tool is that you can use additional data to analyze your code. In a simple case, you might build the code directory, provide the required input type, and indicate the return type. However, you