當從ArrayList <Area>以外的區域訪問區域的邊界時，收到的矩形不正確

Question

我已經完成了多次該代碼，但似乎無法理解它的行爲。

我在添加許多Area實例到ArrayList for循環，同時也產生另一個Area這是所有那些添加到陣列（然而這汞齊化Area從不加入到ArrayList）的合併。

當試圖從另一個類中檢索ArrayList的第一項時，它會給我合併的Area的邊界，它從來沒有添加過！？！？！

import java.awt.Shape; 
import java.awt.geom.Area; 
import java.awt.geom.Rectangle2D; 
import java.util.ArrayList; 


public class CorruptArray { 
public ArrayList<Area> arrayList = new ArrayList<Area>(); 

public CorruptArray(){ 
     double x = 100.0; 
     double y = 200.0; 
     double width = 100.0; 
     double height = 200.0; 
     Area map = null; 

     int i = 5; 
     for(int j =0 ; j<i; j++){ 
      arrayList.add(new Area(new Rectangle2D.Double(x,y,width,height))); 

      x+=10; 
      y+=10; 
      width+=10; 
      height+=10; 
     } 

     int k = 0; 
     for(Area area : arrayList){ 
      System.out.println("INITIAL BOUNDS ON ENTRY: " + area.getBounds().toString()); 
      if(k == 0){ 
       map = area; 
       k++; 

      }else{ 
       map.add(area); 

      } 
      System.out.println("OVERALL JOINED AREA - map " + map.getBounds().toString() + "\n"); 
     } 

     TestArray test = new TestArray(this); 
    } 

private static class TestArray{ 
    TestArray(CorruptArray ca){ 
     System.out.println("\n\n"); 
     for(Area area : ca.arrayList){ 
      System.out.println("RETRIVAL OF BOUNDS FROM TestArray: " + area.getBounds().toString()); 
     } 
    } 
} 



public static void main(String args[]){ 
    new CorruptArray(); 
} 

運行程序時，這是輸出I得到：

INITIAL BOUNDS ON ENTRY: java.awt.Rectangle[x=100,y=200,width=100,height=200] 
OVERALL JOINED AREA - map java.awt.Rectangle[x=100,y=200,width=100,height=200] 

INITIAL BOUNDS ON ENTRY: java.awt.Rectangle[x=110,y=210,width=110,height=210] 
OVERALL JOINED AREA - map java.awt.Rectangle[x=100,y=200,width=120,height=220] 

INITIAL BOUNDS ON ENTRY: java.awt.Rectangle[x=120,y=220,width=120,height=220] 
OVERALL JOINED AREA - map java.awt.Rectangle[x=100,y=200,width=140,height=240] 

INITIAL BOUNDS ON ENTRY: java.awt.Rectangle[x=130,y=230,width=130,height=230] 
OVERALL JOINED AREA - map java.awt.Rectangle[x=100,y=200,width=160,height=260] 

INITIAL BOUNDS ON ENTRY: java.awt.Rectangle[x=140,y=240,width=140,height=240] 
OVERALL JOINED AREA - map java.awt.Rectangle[x=100,y=200,width=180,height=280] 




RETRIVAL OF BOUNDS FROM TestArray: java.awt.Rectangle[x=100,y=200,width=180,height=280] 
RETRIVAL OF BOUNDS FROM TestArray: java.awt.Rectangle[x=110,y=210,width=110,height=210] 
RETRIVAL OF BOUNDS FROM TestArray: java.awt.Rectangle[x=120,y=220,width=120,height=220] 
RETRIVAL OF BOUNDS FROM TestArray: java.awt.Rectangle[x=130,y=230,width=130,height=230] 
RETRIVAL OF BOUNDS FROM TestArray: java.awt.Rectangle[x=140,y=240,width=140,height=240] 

Answer 1

您不添加汞混合區，但你從ArrayList中採取的第一個區域並對其進行修改。它發生在眼前：

if (k == 0) { 
    map = area; 

後來你從列表添加到地圖的其他領域 - 這是名單上的第一個區域。您可能希望基於第一個從列表，而不是創建一個新面積：

if (k == 0) { 
    map = new Area(area);