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This article mainly shows you the "sample analysis of the principle of Builder in java", which is easy to understand and clear. I hope it can help you solve your doubts. Let the editor lead you to study and study the "sample analysis of the principle of Builder in java".

First, give an example of a simple Builder design pattern:

The main implementation class code is as follows:

/ * entity class contains a static inner class Builder * / public class CompanyClient {public String companyName; / / constant denoted by member variables modified by final, which can only be assigned once, and the value cannot be changed after assignment! There are three types of variables modified by final: static variables, instance variables, and local variables. Public String companyAddress; public double companyRegfunds; public String mPerson; public String mType; / / Construction method public CompanyClient () {this (new Builder ());} / / Construction method public CompanyClient (Builder builder) {this.companyName = builder.companyName; this.companyAddress = builder.companyAddress; this.companyRegfunds = builder.companyRegfunds; this.mPerson = builder.person This.mType = builder.type;} public String getCompanyName () {return companyName;} public String getCompanyAddress () {return companyAddress;} public double getCompanyRegfunds () {return companyRegfunds;} public String getmPerson () {return mPerson;} public String getmType () {return mType } public Builder newBuilder () {return newBuilder (this);} @ Override / / when the toString method is overridden, the toString () method is called by default when print this object. Public String toString () {return "CompanyClient {" + "companyName='" + companyName +'\'+ ", companyAddress='" + companyAddress +'\'+ ", companyRegfunds=" + companyRegfunds + "10 million" + ", mPerson=" + mPerson + ", mType='" + mType +'\'+'}' } / * static inner class Builder * / public static class Builder {public String companyName; public String companyAddress; public double companyRegfunds; public String person; public String type; / / constructor public Builder () {companyName = companyName; companyAddress = companyAddress; companyRegfunds = companyRegfunds; person = person Type = type;} / / Construction method Builder (CompanyClient companyClient) {this.companyName = companyClient.companyName; this.companyAddress = companyClient.companyAddress; this.companyRegfunds = companyClient.companyRegfunds; this.person = companyClient.mPerson; this.type = companyClient.mType } public Builder setCompanyName (String name) {companyName = name; return this;} public Builder setCompanyAddress (String address) {companyAddress = address; return this;} public Builder setCompanyRegfunds (double regfunds) {companyRegfunds = regfunds; return this } public Builder setmPerson (String per) {person = per; return this;} public Builder setmType (String typeStr) {type = typeStr; return this;} / / build an entity public CompanyClient build () {return new CompanyClient (this);}

The implementation code of the test class is as follows:

Public class TestBuilder {public static void main (String [] args) {CompanyClient client = new CompanyClient.Builder () .setCompanyName ("alibaba") .setCompanyAddress ("wangjing") .setCompanyRegfunds (5) .setmPerson ("10000") .build (); System.out.println (client) System.out.println ("-"); CompanyClient.Builder builder = new CompanyClient.Builder (); builder.setCompanyName ("huawei"); builder.setCompanyAddress ("haidian"); builder.setCompanyRegfunds (20); builder.setmType ("communication"); CompanyClient client1 = builder.build (); System.out.println (client1) System.out.println ("-"); CompanyClient.Builder build1 = client1.newBuilder (); build1.setCompanyName ("baidu"); CompanyClient client2 = build1.build (); System.out.println (client2);}}

The output is as follows:

CompanyClient {companyName='alibaba', companyAddress='wangjing', companyRegfunds= 50 million, mPerson=10000, mType='null'}-CompanyClient {companyName='huawei', companyAddress='haidian', companyRegfunds= 200 million, mPerson=null, mType='communication'}-CompanyClient {companyName='baidu', companyAddress='haidian', companyRegfunds= 200 million, mPerson=null, mType='communication'}

First look at the first line of code in the main function:

CompanyClient client = new CompanyClient.Builder () .setCompanyName ("alibaba") .setCompanyAddress ("wangjing") .setCompanyRegfunds (5) .setmPerson ("10000") .build ()

The reason why this can be done is that the internal static class Builder defines a variable that is exactly the same as the CompanyClient class, which sets the property value through a series of member functions, but the return value is this, that is, all Builder objects. Finally, a build function is provided to create the CompanyClient object, and the CompanyClient object is returned. The corresponding constructor is defined in the CompanyClient class, that is, the input parameter of the constructor is the Builder object. Then assign values to your own member variables in turn, and the corresponding values are all values in the Builder object. In addition, another function of the member function in the Builder class that returns the Builder object itself is to make it support chained calls, making the code much more readable.

To sum up, the builder design pattern in Java environment:

Define a static inner class Builder with the same member variables as the external class

The Builder class uses a series of methods to assign member variables and returns the current object itself (this).

The Builder class provides a build method or a create method for creating the corresponding external class. The method invokes a private constructor of the external class, whose argument is the inner class Builder.

The outer class provides a private constructor for the inner class to call. In this constructor, the member variable is assigned to the corresponding value in the Builder object.

The above is all the contents of the article "sample Analysis of Builder principles in java". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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