作用：
组装具有复杂结构的实例，组装的过程被隐藏在Director角色中
理解：
当创建的对象特别的复杂，把这个复杂的对象进行拆分。这个复杂对象的各个部分经常会需要面临剧烈的变化，但是他们的组合在一起的算法是相对稳定的。
Builder模式就是一种“封装机制”来隔离“复杂对象的各个部分”的变化，从而保持系统中的“稳定构建算法”不随需求发生改变而改变。
小案例
Builder.java
package example1;
/**
* @Author:DarknessShadow
* @description:
* @date 2020/5/13 10:19
*/
public abstract class Builder {
public abstract void makeTitle(String title);
public abstract void makeString(String string);
public abstract void makeItems(String[] items);
public abstract void close();
}
HtmlBuilder.java
package example1;
import java.io.FileWriter;
import java.io.PrintWriter;
/**
* @Author:DarknessShadow
* @description:
* @date 2020/5/13 10:41
*/
public class HTMLBuilder extends Builder {
private String filename;
private PrintWriter writer;
@Override
public void makeTitle(String title) {
filename = title + ".html";
try {
writer = new PrintWriter(new FileWriter(filename));
} catch (Exception e) {
e.printStackTrace();
}
writer.println("<html><head><title>" + title + "</title></head><body>");
writer.println("<h1>" + title + "</h1>");
}
@Override
public void makeString(String string) {
writer.println("<p>" + string + "</p>");
}
@Override
public void makeItems(String[] items) {
writer.print("<ul>");
for (int i = 0; i < items.length; i++) {
writer.println("<li>" + items[i] + "</li>");
}
writer.println("</ul");
}
@Override
public void close() {
writer.println("</body></html>");
writer.close();
}
public String getResult() {
return filename;
}
}
TextBuilder.java
package example1;
/**
* @Author:DarknessShadow
* @description:
* @date 2020/5/13 10:25
*/
public class TextBuilder extends Builder{
private StringBuffer buffer = new StringBuffer();
@Override
public void makeTitle(String title) {
buffer.append("==============================
");
buffer.append("[" + title + "]
");
buffer.append("
");
}
@Override
public void makeString(String string) {
buffer.append("@" + string + "
");
buffer.append("
");
}
@Override
public void makeItems(String[] items) {
for (int i = 0; i < items.length; i++) {
buffer.append(" ." + items[i] + "
");
}
buffer.append("
");
}
@Override
public void close() {
buffer.append("==============================
");
}
public String getResult() {
return buffer.toString();
}
}
Director.java
package example1;
/**
* @Author:DarknessShadow
* @description:
* @date 2020/5/13 10:20
*/
public class Director {
private Builder builder;
public Director(Builder builder) {
this.builder = builder;
}
public void construct() {// 编写文档
builder.makeTitle("Greeting"); // 标题
builder.makeString("从早上到下午"); // 字符串
builder.makeItems(new String[]{ // 条目
"good morning",
"good afternoon",
});
builder.makeString("晚上");
builder.makeItems(new String[]{ // 条目
"good night",
"good bye",
});
builder.close();
}
}
Main.java
package example1;
/**
* @Author:DarknessShadow
* @description:
* @date 2020/5/13 10:47
*/
public class Main {
public static void main(String[] args) {
String arg = "plain";
if ("plain".equals(arg)) {
TextBuilder textBuilder = new TextBuilder();
Director director = new Director(textBuilder);
director.construct();
String result = textBuilder.getResult();
System.out.println(result);
} else if ("html".equals(arg)) {
HTMLBuilder htmlBuilder = new HTMLBuilder();
Director director = new Director(htmlBuilder);
director.construct();
String filename = htmlBuilder.getResult();
System.out.println(filename + "文件编写完成");
}
}
}