当前页面: 开发资料首页 → J2SE 专题 → 映射键值问题（大虾一定要帮忙啊！）

映射键值问题（大虾一定要帮忙啊！）

摘要: 映射键值问题（大虾一定要帮忙啊！）

ShapeFactory.java

import java.util.HashMap;
import java.util.Map;
public class ShapeFactory {
public static final int SHAPE_TYPE_CIRCLE=1;
public static final int SHAPE_TYPE_RECTANGLE=2;
public static final int SHAPE_TYPE_LINE=3;
private static Map-#60;Integer,String-#62; Shapes=new HashMap-#60;Integer,String-#62;();
static{
Shapes.put(new Integer(SHAPE_TYPE_CIRCLE),-#34;Circle-#34;);
Shapes.put(new Integer(SHAPE_TYPE_RECTANGLE),-#34;Rectangle-#34;);
Shapes.put(new Integer(SHAPE_TYPE_LINE),-#34;Line-#34;);
}
public static Shape getShape(int type) {
try{
String className=Shapes.get(new Integer(type));

return (Shape)Class.forName(className).newInstance();
}
catch(Exception e) { return null; }
}
}


Panel.java


import java.io.*;
public class Panel {
public void selectShape() throws Exception {
System.out.println(-#34;请输入形状类型:-#34;);
BufferedReader input=new BufferedReader(new InputStreamReader(System.in));
int shapeType=Integer.parseInt(input.readLine());
Shape shape=ShapeFactory.getShape(shapeType);
if(shape==null)
System.out.println(-#34;输入的形状类型不存在-#34;);
else
shape.draw();
}
public static void main(String[] args) throws Exception {
new Panel().selectShape();
}
}


为何我输入1或2或3都提示该形状不存在？看了好久也看不出来啊！！

---

你要返回的是Circle等类的对象,但是实例化的时候没找到这个类,所以返回的是一个null对象.

你当前路径下没有Circle这些类的定义,如果在其它包中,要指定正确的包名.

而且你在异常捕获的时候什么都没做,所以没看出发生了异常.

你可以在catch块中打印一下堆栈信息(e.printStackStrace();)输出的应该是ClassNotFoundException

---

确实如imA(男的不会，会的不男) ( ) 信誉：5 所说，还有4个文件没通过编译，因为没有包

含它们，所以也没通过编译，然后把这些文件全放到ShapeFoctory.java 中就可以了：


import java.util.HashMap;
import java.util.Map;
public class ShapeFactory {
public static final int SHAPE_TYPE_CIRCLE=1;
public static final int SHAPE_TYPE_RECTANGLE=2;
public static final int SHAPE_TYPE_LINE=3;
private static Map-#60;Integer,String-#62; Shapes=new HashMap-#60;Integer,String-#62;();
static{
Shapes.put(new Integer(SHAPE_TYPE_CIRCLE),-#34;Circle-#34;);
Shapes.put(new Integer(SHAPE_TYPE_RECTANGLE),-#34;Rectangle-#34;);
Shapes.put(new Integer(SHAPE_TYPE_LINE),-#34;Line-#34;);
}
public static Shape getShape(int type) {
try{
String className=Shapes.get(new Integer(type));

return (Shape)Class.forName(className).newInstance();
}
catch(Exception e) { return null; }
}
}

abstract class Shape {
abstract void draw();
}

class Circle extends Shape {
public void draw() {
System.out.println(-#34;draw a circle-#34;);
}
}

class Line extends Shape {
public void draw() {
System.out.println(-#34;draw a line-#34;);
}
}

class Rectangle extends Shape {
public void draw() {
System.out.println(-#34;draw a rectangle-#34;);
}
}

---