问答题

请完成下列Java程序。程序的功能是利用迭代法求一个数的平方根(求平方根的迭代公式为: Xn+1=1/2(Xn+a/Xn))。 注意:请勿改动main()主方法和其他已有的语句内容,仅在下划线处填入适当的语句。 源程序代码文件清单如下: public class PingFangGen { public static void main(String args[ ]) { System.out.println(Math.sqrt(2.0)); } static double sqrt(______) { double x=1.0; do{ ______; } while(Math.abs(x*x-a)/a>1e-6); return x; } }

【参考答案】

double ax=(x+a/x)[解析] 本题主要考查do-while循环语句及Java的基本运算。解答本题需要对do......

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下面是一个Applet程序,实现实心或者空心矩形的绘制。要求鼠标在Applet窗口中拖动实现矩形的绘制,可以选择填充或者空心,按钮用来清空窗口中的图像。请改正程序中的错误(有下划线的语句),使程序能输出正确的结果。注意:不改动程序的结构,不得增行或删行。源程序代码文件清单如下:import java.awt.*;import java.applet.*; *<applet code= ex16_3.class width=800 height=400>< applet>* public class ex16_3 extends Applet{private Button btnClear;private CheckboxGroup cbg;private Checkbox chk1, chk2;private int upX, upY;private int downX, downY;private boolean bDraw, bClear, bStyle;public void init(){bDraw = false;bClear = false;bStyle = false;setLayout(null);cbg = new CheckboxGroup();chk1 = new Checkbox( Hollow , cbg, true);chk2 = new Checkbox( Filled , cbg, false);chk1.reshape(80,getSize().height-80,80,25);chk2.reshape(160,getSize().height-80,80,25);add(chk1);add(chk2);btnClear = new Button( ctear );btnClear.reshape(240,getSize().height-80,80,25);add(btnClear);}public void paint(Graphics g){if (bDraw){if(upX>downX && upY>downY){if(bStyle)g.fillRect(downX, downY, upX-downX, upY-downY);elseg.drawRect(downX, downY, upX-downX, upY-downY);}else if(upX>downX&&upY<downY){if(bStyle)g.fillRect(downX, upY, upX-downX, downY-upY);elseg.drawRect(downX, upY, upX - downX, downY - upY);}else if(upX<downX && upY>downY){if(bStyle)g.fillRect(upX, downY, downX-upX, upY-downY);elseg.drawRect(upX, downY, downX-upX, upY-downY);}else if(upX<downX && upY<downY){if(bStyle)g.fillRect(upX, upY, downX-upX, downY-upY);elseg.drawRect(upX, upY, downX-upX, downY-upY);}bDraw = false;}if (bClear){g.clearRect(0,0, getSize().height, getSize().width);bClear = false;}}public void update(Graphics g){paint(g);}public boolean mouseUp(Event e, int x, int y){upX=x;upY=y;bDraw=true;repaint();return true;}public boolean mouseDown(Event e, int x, int y){downX=x;downY=y;return true;}public boolean action(Event e, Object o){if(e.target==btnClear){bClear=true;repaint();}if(chk1.getState()==true){bStyle=true;}if(chk2.getState()==true){bStyle=false;}return true;}}ex9_3.html<HTML><HEAD><TITLE>ex9_3< TITLE>< HEAD><BODY><applet code= ex9_3.class width=800 height=400>< applet>< BODY>< HTML>