错在哪里？

[lion222]

出现error:
ArtTracer.java:56: missing return statment
public Diagram createDiagram(String order){
1 error

应该怎么办？

我的程序是这样的：

interface Diagram {
public void draw();
public void erase();
}
class Round implements Diagram{
Round(){
draw();
erase();
}
public void draw(){
System.out.println("round is drawing!");
}
public void erase(){
System.out.println("round is erasing!");
}
}
class Square implements Diagram{
Square(){
draw();
erase();
}
public void draw(){
System.out.println("Square is drawing!");
}
public void erase(){
System.out.println("Square is erasing!");
}
}
class Trigon implements Diagram{
Trigon(){
draw();
erase();
}
public void draw(){
System.out.println("Trigon is drawing!");
}
public void erase(){
System.out.println("Trigon is erasing!");
}
}
/*
class BadShapeException extends Exception{
public BadShapeException(String msg){
super(msg);
}
}
*/
public class ArtTracer{
private String message=null;
ArtTracer (){
this.message=" you are wrong!";
}
ArtTracer (String message){
this.message=message;
}
public Diagram createDiagram(String order){
if (order.equalsIgnoreCase("round")){
return new Round();
}
else if (order.equalsIgnoreCase("square")){
return new Square();
}
else if (order.equalsIgnoreCase("trigon")){
return new Trigon();
}
/*
else{
throw new BadShapeException("You can't do that");
}
*/
}
public static void main(String args[]){
String message=args[0];
ArtTracer artTracer=null;
artTracer=new ArtTracer(message);
artTracer.createDiagram(message);
}


}

[gdsean]

public Diagram createDiagram(String order){
if (order.equalsIgnoreCase("round")){
return new Round();
}
else if (order.equalsIgnoreCase("square")){
return new Square();
}
else if (order.equalsIgnoreCase("trigon")){
return new Trigon();
}
这里缺少返回，如果条件都不满足你返回什么Diagram呢
}

[robingranite]

修改ArtTracer类：
添加：
private Diagram diagram = null;

修改createDiagram()方法，在每个if块里面的return修改为：
diagram = new Round();或者
diagram = new Square();或者
diagram = new Trigon()

然后在该方法的最后添加：
return diagram;

[lovefeng]

必须在任何情况下都有返回值

[lion222]

谢谢各位的回答。:)

[lion222]

若分少了，可与我联系，我会再加。谢谢！
:)