java.lang.nullpointerexception是什么意思？java 二分法排序

public class NullPointerExceptionextends RuntimeException《/dt》当应用程序试图在需要对象的地方使用 null 时，抛出该异常。这种情况包括： 调用 null 对象的实例方法。 访问或修改 null 对象的字段。 将 null 作为一个数组，获得其长度。 将 null 作为一个数组，访问或修改其时间片。 将 null 作为 Throwable 值抛出。 应用程序应该抛出该类的实例，指示其他对 null 对象的非法使用。

public class Lookup { /** * @param args */ public static void main(String args) { // TODO Auto-generated method stub /** * 二分法查找 */ int a={23,45,98,100,110,120,140}; int search=120;//记录要查找的元素 int lower=0;//记录第一个元素 int temp=a.length-1 ; int index=-1; while(lower《=temp){ index = (lower+temp)/2;//记录中间元素，用两边之和除2. int currentValue=a[index]; if(currentValue==search){//如果得到的数与要查找的数相等则break退出; break; }else if(currentValue《search){//如果得到的数要小于查找的数、就用下标加1;否则减一 lower=index+1; }else{ temp = index-1; } } if(lower《=temp){ System.out.println(search+“在数组中第：“+(index+1)+“位“); }else{ System.out.println(“里面没有这个元素“); } }}

import java.awt.*; import java.awt.event.*; //俄罗斯方块类 public class computer extends Frame{ public static boolean isPlay=false; public static int level=1,score=0; public static TextField scoreField,levelField;public static MyTimer timer; GameCanvas gameScr;public static void main(String argus){ computer ers = new computer(“俄罗斯方块游戏 V1.0 Author:Vincent“); WindowListener win_listener = new WinListener(); ers.addWindowListener(win_listener); }//俄罗斯方块类的构造方法 computer(String title){ super(title);setSize(600,480); setLayout(new GridLayout(1,2));gameScr = new GameCanvas(); gameScr.addKeyListener(gameScr);timer = new MyTimer(gameScr); timer.setDaemon(true); timer.start(); timer.suspend();add(gameScr);Panel rightScr = new Panel(); rightScr.setLayout(new GridLayout(2,1,0,30)); rightScr.setSize(120,500); add(rightScr);//右边信息窗体的布局 MyPanel infoScr = new MyPanel(); infoScr.setLayout(new GridLayout(4,1,0,5)); infoScr.setSize(120,300); rightScr.add(infoScr);//定义标签和初始值 Label scorep = new Label(“分数:“,Label.LEFT); Label levelp = new Label(“级数:“,Label.LEFT); scoreField = new TextField(8); levelField = new TextField(8); scoreField.setEditable(false); levelField.setEditable(false); infoScr.add(scorep); infoScr.add(scoreField); infoScr.add(levelp); infoScr.add(levelField); scorep.setSize(new Dimension(20,60)); scoreField.setSize(new Dimension(20,60)); levelp.setSize(new Dimension(20,60)); levelField.setSize(new Dimension(20,60)); scoreField.setText(“0“); levelField.setText(“1“);//右边控制按钮窗体的布局 MyPanel controlScr = new MyPanel(); controlScr.setLayout(new GridLayout(5,1,0,5)); rightScr.add(controlScr);//定义按钮play Button play_b = new Button(“开始游戏“); play_b.setSize(new Dimension(50,200)); play_b.addActionListener(new Command(Command.button_play,gameScr));//定义按钮Level UP Button level_up_b = new Button(“提高级数“); level_up_b.setSize(new Dimension(50,200)); level_up_b.addActionListener(new Command(Command.button_levelup,gameScr));//定义按钮Level Down Button level_down_b =new Button(“降低级数“); level_down_b.setSize(new Dimension(50,200)); level_down_b.addActionListener(new Command(Command.button_leveldown,gameScr));//定义按钮Level Pause Button pause_b =new Button(“游戏暂停“); pause_b.setSize(new Dimension(50,200)); pause_b.addActionListener(new Command(Command.button_pause,gameScr));//定义按钮Quit Button quit_b = new Button(“退出游戏“); quit_b.setSize(new Dimension(50,200)); quit_b.addActionListener(new Command(Command.button_quit,gameScr));controlScr.add(play_b); controlScr.add(level_up_b); controlScr.add(level_down_b); controlScr.add(pause_b); controlScr.add(quit_b); setVisible(true); gameScr.requestFocus(); } }//重写MyPanel类，使Panel的四周留空间 class MyPanel extends Panel{ public Insets getInsets(){ return new Insets(30,50,30,50); } }//游戏画布类 class GameCanvas extends Canvas implements KeyListener{ final int unitSize = 30; //小方块边长 int rowNum; //正方格的行数 int columnNum; //正方格的列数 int maxAllowRowNum; //允许有多少行未削 int blockInitRow; //新出现块的起始行坐标 int blockInitCol; //新出现块的起始列坐标 int scrArr; //屏幕数组 Block b; //对方快的引用//画布类的构造方法 GameCanvas(){ rowNum = 15; columnNum = 10; maxAllowRowNum = rowNum - 2; b = new Block(this); blockInitRow = rowNum - 1; blockInitCol = columnNum/2 - 2; scrArr = new int ; }//初始化屏幕，并将屏幕数组清零的方法 void initScr(){ for(int i=0;i《rowNum;i++) for (int j=0; j《columnNum;j++) scrArr[i][j]=0; b.reset(); repaint(); }//重新刷新画布方法 public void paint(Graphics g){ for(int i = 0; i 《 rowNum; i++) for(int j = 0; j 《 columnNum; j++) drawUnit(i,j,scrArr[i][j]); }//画方块的方法 public void drawUnit(int row,int col,int type){ scrArr[row][col] = type; Graphics g = getGraphics(); switch(type){ //表示画方快的方法 case 0: g.setColor(Color.black);break; //以背景为颜色画 case 1: g.setColor(Color.blue);break; //画正在下落的方块 case 2: g.setColor(Color.magenta);break; //画已经落下的方法 } g.fill3DRect(col*unitSize,getSize().height-(row+1)*unitSize,unitSize,unitSize,true); g.dispose(); }public Block getBlock(){ return b; //返回block实例的引用 }//返回屏幕数组中(row,col)位置的属性值 public int getScrArrXY(int row,int col){ if (row 《 0 || row 》= rowNum || col 《 0 || col 》= columnNum) return(-1); else return(scrArr[row][col]); }//返回新块的初始行坐标方法 public int getInitRow(){ return(blockInitRow); //返回新块的初始行坐标 }//返回新块的初始列坐标方法 public int getInitCol(){ return(blockInitCol); //返回新块的初始列坐标 }//满行删除方法 void deleteFullLine(){ int full_line_num = 0; int k = 0; for (int i=0;i《rowNum;i++){ boolean isfull = true;L1:for(int j=0;j《columnNum;j++) if(scrArr[i][j] == 0){ k++; isfull = false; break L1; } if(isfull) full_line_num++; if(k!=0 && k-1!=i && !isfull) for(int j = 0; j 《 columnNum; j++){ if (scrArr[i][j] == 0) drawUnit(k-1,j,0); else drawUnit(k-1,j,2); scrArr[k-1][j] = scrArr[i][j]; } } for(int i = k-1 ;i 《 rowNum; i++){ for(int j = 0; j 《 columnNum; j++){ drawUnit(i,j,0); scrArr[i][j]=0; } } computer.score += full_line_num; computer.scoreField.setText(““+computer.score); }//判断游戏是否结束方法 boolean isGameEnd(){ for (int col = 0 ; col 《columnNum; col ++){ if(scrArr[maxAllowRowNum][col] !=0) return true; } return false; }public void keyTyped(KeyEvent e){ }public void keyReleased(KeyEvent e){ }//处理键盘输入的方法 public void keyPressed(KeyEvent e){ if(!computer.isPlay) return; switch(e.getKeyCode()){ case KeyEvent.VK_DOWN:b.fallDown();break; case KeyEvent.VK_LEFT:b.leftMove();break; case KeyEvent.VK_RIGHT:b.rightMove();break; case KeyEvent.VK_SPACE:b.leftTurn();break; } } }//处理控制类 class Command implements ActionListener{ static final int button_play = 1; //给按钮分配编号 static final int button_levelup = 2; static final int button_leveldown = 3; static final int button_quit = 4; static final int button_pause = 5; static boolean pause_resume = true;int curButton; //当前按钮 GameCanvas scr;//控制按钮类的构造方法 Command(int button,GameCanvas scr){ curButton = button; this.scr=scr; }//按钮执行方法 public void actionPerformed (ActionEvent e){ switch(curButton){ case button_play:if(!computer.isPlay){ scr.initScr(); computer.isPlay = true; computer.score = 0; computer.scoreField.setText(“0“); computer.timer.resume(); } scr.requestFocus(); break; case button_levelup:if(computer.level 《 10){ computer.level++; computer.levelField.setText(““+computer.level); computer.score = 0; computer.scoreField.setText(““+computer.score); } scr.requestFocus(); break; case button_leveldown:if(computer.level 》 1){ computer.level--; computer.levelField.setText(““+computer.level); computer.score = 0; computer.scoreField.setText(““+computer.score); } scr.requestFocus(); break; case button_pause:if(pause_resume){ computer.timer.suspend(); pause_resume = false; }else{ computer.timer.resume(); pause_resume = true; } scr.requestFocus(); break; case button_quit:System.exit(0); } } }//方块类 class Block { static int pattern = { {0x0f00,0x4444,0x0f00,0x4444},//用十六进至表示，本行表示长条四种状态 {0x04e0,0x0464,0x00e4,0x04c4}, {0x4620,0x6c00,0x4620,0x6c00}, {0x2640,0xc600,0x2640,0xc600}, {0x6220,0x1700,0x2230,0x0740}, {0x6440,0x0e20,0x44c0,0x8e00}, {0x0660,0x0660,0x0660,0x0660} }; int blockType; //块的模式号（0-6） int turnState; //块的翻转状态（0-3） int blockState; //快的下落状态 int row,col; //块在画布上的坐标 GameCanvas scr;//块类的构造方法 Block(GameCanvas scr){ this.scr = scr; blockType = (int)(Math.random() * 1000)%7; turnState = (int)(Math.random() * 1000)%4; blockState = 1; row = scr.getInitRow(); col = scr.getInitCol(); }//重新初始化块，并显示新块 public void reset(){ blockType = (int)(Math.random() * 1000)%7; turnState = (int)(Math.random() * 1000)%4; blockState = 1; row = scr.getInitRow(); col = scr.getInitCol(); dispBlock(1); }//实现“块”翻转的方法 public void leftTurn(){ if(assertValid(blockType,(turnState + 1)%4,row,col)){ dispBlock(0); turnState = (turnState + 1)%4; dispBlock(1); } }//实现“块”的左移的方法 public void leftMove(){ if(assertValid(blockType,turnState,row,col-1)){ dispBlock(0); col--; dispBlock(1); } }//实现块的右移 public void rightMove(){ if(assertValid(blockType,turnState,row,col+1)){ dispBlock(0); col++; dispBlock(1); } }//实现块落下的操作的方法 public boolean fallDown(){ if(blockState == 2) return(false); if(assertValid(blockType,turnState,row-1,col)){ dispBlock(0); row--; dispBlock(1); return(true); }else{ blockState = 2; dispBlock(2); return(false); } }//判断是否正确的方法 boolean assertValid(int t,int s,int row,int col){ int k = 0x8000; for(int i = 0; i 《 4; i++){ for(int j = 0; j 《 4; j++){ if((int)(pattern[t][s]&k) != 0){ int temp = scr.getScrArrXY(row-i,col+j); if (temp《0||temp==2) return false; } k = k 》》 1; } } return true; }//同步显示的方法 public synchronized void dispBlock(int s){ int k = 0x8000; for (int i = 0; i 《 4; i++){ for(int j = 0; j 《 4; j++){ if(((int)pattern[blockType][turnState]&k) != 0){ scr.drawUnit(row-i,col+j,s); } k=k》》1; } } } }//定时线程 class MyTimer extends Thread{ GameCanvas scr;public MyTimer(GameCanvas scr){ this.scr = scr; }public void run(){ while(true){ try{ sleep((10-computer.level + 1)*100); } catch(InterruptedException e){} if(!scr.getBlock().fallDown()){ scr.deleteFullLine(); if(scr.isGameEnd()){ computer.isPlay = false; suspend(); }else scr.getBlock().reset(); } } } }class WinListener extends WindowAdapter{ public void windowClosing (WindowEvent l){ System.exit(0); } }