Java Builder Pattern Detailed explanation and examples of builder pattern

Java Builder Pattern

1. Concept

Separate a complex build from its representation, so that the same build process can create different representations. [Separation of construction and presentation, different representations for the same construction]

The difference between it and the abstract factory: In the builder pattern, there is a mentor, who manages the builder, and the user is in contact with the mentor. The mentor contacts the builder and ends up with the product. That is, the construction mode can enforce a step-by-step construction process.

The construction mode encapsulates complex internal creation internally. For external callers, they only need to pass in the builder and construction tools. The caller does not need to care about how the finished product is built internally.

Take a simple example, such as a car. There are many parts, such as wheels, steering wheels, engines, and various small parts, etc. There are many parts, but there are far more than these. How to assemble these parts into a car? This assembly process is also very complicated (requiring good assembly technology). The builder mode is to combine components and groups

2. UML diagram

3. Code

public interface Builder { 
　　　void buildPartA(); 
　　　void buildPartB(); 
　　　void buildPartC(); 
　
　　　Product getResult(); 
　} 
 
 //具体建造工具
　public class ConcreteBuilder implements Builder { 
　　　Part partA, partB, partC; 
 
　　　public void buildPartA() {
　　　　　//这里是具体如何构建partA的代码
　　　}; 
　　　public void buildPartB() { 
　　　　　//这里是具体如何构建partB的代码
　　　}; 
　　　 public void buildPartC() { 
　　　　　//这里是具体如何构建partB的代码
　　　}; 
　　　 public Product getResult() { 
　　　　　//返回最后组装成品结果
　　　}; 
　}
 
 //建造者
　public class Director {
　　　private Builder builder; 
　
　　　public Director( Builder builder ) { 
　　　　　this.builder = builder; 
　　　} 
　　　public void construct() { 
　　　　　builder.buildPartA();
　　　　　builder.buildPartB();
　　　　　builder.buildPartC(); 
　　　} 
　} 
 
 
　public interface Product { }
　public interface Part { }

The following is the method of calling builder:

ConcreteBuilder builder = new ConcreteBuilder();
Director director = new Director( builder );
 
director.construct();
Product product = builder.getResult();

4. Application scenario

This mode is used by JavaMail in Java applications.

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