一:概述
Builder模式定义:
将一个复杂对象的构建与它的表示分离,使得同样的构建过程可以创建不同的表示.
Builder模式是一步一步创建一个复杂的对象,它允许用户可以只通过指定复杂对象的类型和内容就可以构建它们.用户不知道内部的具体构建细节.
先,需要一个接口,它定义如何创建复杂对象的各个部件:
public interface Builder { //创建部件A 比如创建汽车车轮 } |
用Director构建最后的复杂对象,而在上面Builder接口中封装的是如何创建一个个部件(复杂对象是由这些部件组成的),也就是说Director的内容是如何将部件最后组装成成品:
public class Director { private Builder builder;
扫描二维码关注公众号,回复:
1127900 查看本文章
public Director( Builder builder ) { } } |
Builder的具体实现ConcreteBuilder:
通过具体完成接口Builder来构建或装配产品的部件;
定义并明确它所要创建的是什么具体东西;
提供一个可以重新获取产品的接口:
public class ConcreteBuilder implements Builder { Part partA, partB, partC; } |
复杂对象:产品Product:
public interface Product { } |
复杂对象的部件:
public interface Part { } |
调用Builder模式:
|
2、需要生成的产品对象的属性相互依赖,建造者模式可以强迫生成顺序。
3、在对象创建过程中会使用到系统中的一些其它对象,这些对象在产品对象的创建过程中不易得到。
public final class StringBuilder extends AbstractStringBuilder implements java.io.Serializable, CharSequence { /** use serialVersionUID for interoperability */ static final long serialVersionUID = 4383685877147921099L; /** * Constructs a string builder with no characters in it and an * initial capacity of 16 characters. */ public StringBuilder() { super(16); } /** * Constructs a string builder with no characters in it and an * initial capacity specified by the <code>capacity</code> argument. * * @param capacity the initial capacity. * @throws NegativeArraySizeException if the <code>capacity</code> * argument is less than <code>0</code>. */ public StringBuilder(int capacity) { super(capacity); }
abstract class AbstractStringBuilder implements Appendable, CharSequence { /** * The value is used for character storage. */ char value[]; /** * The count is the number of characters used. */ int count; /** * This no-arg constructor is necessary for serialization of subclasses. */ AbstractStringBuilder() { } /** * Creates an AbstractStringBuilder of the specified capacity. */ AbstractStringBuilder(int capacity) { value = new char[capacity]; } /** * Returns the length (character count). * * @return the length of the sequence of characters currently * represented by this object */ public int length() { return count; } /** * Returns the current capacity. The capacity is the amount of storage * available for newly inserted characters, beyond which an allocation * will occur. * * @return the current capacity */ public int capacity() { return value.length; }