关于java强制类型转换的溢出问题 --- 求解
package day02all.day02.copy;
/** 类型转换的演示 */
public class CastDemo {
public static void main(String[] args){
long l = 65536 + 1024 + 512 + 8;
// 000000 ....... 00000001 00000110 00001000
byte b = (byte)l;//
System.out.println(b);//8
//强制类型转换会造成数据的损失.精度缺失
double pi = 3.1415926535897932384;
System.out.println(pi);
float f = (float)pi;
System.out.println(f);
double d = Math.sqrt(2);//开平方
float f1 = (float)d;
System.out.println(d);
System.out.println(f1);
//price 价格
}
}
8
3.141592653589793
3.1415927//（1）
1.4142135623730951
1.4142135（2）
问题：为什么（1）和（2）一个产生进位一个不产生进位？
详细讲解下关于计算机如何处理溢出的问题。
[解决办法]
这个问题还一直没注意过，只知道double转float会发生精度丢失，具体会如何丢失还真没仔细研究过
借LZ的问题调查了一下，把2进制打出来试试看了看
- Java code
double pi = 3.1415926535897932384;//System.out.println(pi);float f = (float)pi;//System.out.println(f);String sd = Long.toBinaryString(Double.doubleToLongBits(pi));System.out.printf("%64s\n", sd);System.out.printf("%64s\n", sd.substring(12));String sf = Integer.toBinaryString(Float.floatToIntBits(f));System.out.printf("%32s\n", sf);System.out.printf("%32s\n", sf.substring(9));System.out.printf("%s\n", sd.substring(12));System.out.printf("%s\n", sf.substring(9));System.out.println(); double d = Math.sqrt(2);float f1 = (float)d;//System.out.println(d);//System.out.println(f1);sd = Long.toBinaryString(Double.doubleToLongBits(d));System.out.printf("%64s\n", sd);System.out.printf("%64s\n", sd.substring(12));sf = Integer.toBinaryString(Float.floatToIntBits(f1));System.out.printf("%32s\n", sf);System.out.printf("%32s\n", sf.substring(9));System.out.printf("%s\n", sd.substring(12));System.out.printf("%s\n", sf.substring(9));打印结果 100000000001001001000011111101101010100010001000010110100011000 001001000011111101101010100010001000010110100011000 1000000010010010000111111011011 00100100001111110110110010010000111111011010101000100010000101101000110000010010000111111011011 11111111110110101000001001111001100110011111110011101111001101 10101000001001111001100110011111110011101111001101 111111101101010000010011110011 10101000001001111001110101000001001111001100110011111110011101111001101101010000010011110011
[解决办法]
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.*;
import javax.swing.Timer;
public class Tetris extends JFrame {
public Tetris() {
Tetrisblok a = new Tetrisblok();
addKeyListener(a);
add(a);
}
public static void main(String[] args) {
Tetris frame = new Tetris();
JMenuBar menu = new JMenuBar();
frame.setJMenuBar(menu);
JMenu game = new JMenu("游戏");
JMenuItem newgame = game.add("新游戏");
JMenuItem pause = game.add("暂停");
JMenuItem goon = game.add("继续");
JMenuItem exit = game.add("退出");
JMenu help = new JMenu("帮助");
JMenuItem about = help.add("关于");
menu.add(game);
menu.add(help);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(220, 275);
frame.setTitle("Tetris内测版");
// frame.setUndecorated(true);
frame.setVisible(true);
frame.setResizable(false);
}
}
// 创建一个俄罗斯方块类
class Tetrisblok extends JPanel implements KeyListener {
// blockType 代表方块类型
// turnState代表方块状态
private int blockType;
private int score = 0;
private int turnState;
private int x;
private int y;
private int i = 0;
int j = 0;
int flag = 0;
// 定义已经放下的方块x=0-11,y=0-21;
int[][] map = new int[13][23];
// 方块的形状 第一组代表方块类型有S、Z、L、J、I、O、T 7种 第二组 代表旋转几次 第三四组为 方块矩阵
private final int shapes[][][] = new int[][][] {
// i
{ { 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0 },
{ 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0 } },
// s
{ { 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0 },
{ 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0 } },
// z
{ { 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0 },
{ 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0 } },
// j
{ { 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0 },
{ 1, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 1, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0 },
{ 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 } },
// o
{ { 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 } },
// l
{ { 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0 },
{ 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 } },
// t
{ { 0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0 },
{ 1, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0 } } };
// 生成新方块的方法
public void newblock() {
blockType = (int) (Math.random() * 1000) % 7;
turnState = (int) (Math.random() * 1000) % 4;
x = 4;
y = 0;
if (gameover(x, y) == 1) {
newmap();
drawwall();
score = 0;
JOptionPane.showMessageDialog(null, "GAME OVER");
}
}
// 画围墙
public void drawwall() {
for (i = 0; i < 12; i++) {
map[i][21] = 2;
}
for (j = 0; j < 22; j++) {
map[11][j] = 2;
map[0][j] = 2;
}
}
// 初始化地图
public void newmap() {
for (i = 0; i < 12; i++) {
for (j = 0; j < 22; j++) {
map[i][j] = 0;
}
}
}
// 初始化构造方法
Tetrisblok() {
newblock();
newmap();
drawwall();
Timer timer = new Timer(1000, new TimerListener());
timer.start();
}
// 旋转的方法
public void turn() {
int tempturnState = turnState;
turnState = (turnState + 1) % 4;
if (blow(x, y, blockType, turnState) == 1) {
}
if (blow(x, y, blockType, turnState) == 0) {
turnState = tempturnState;
}
repaint();
}
// 左移的方法
public void left() {
if (blow(x - 1, y, blockType, turnState) == 1) {
x = x - 1;
}
;
repaint();
}
// 右移的方法
public void right() {
if (blow(x + 1, y, blockType, turnState) == 1) {
x = x + 1;
}
;
repaint();
}
// 下落的方法
public void down() {
if (blow(x, y + 1, blockType, turnState) == 1) {
y = y + 1;
delline();
}
;
if (blow(x, y + 1, blockType, turnState) == 0) {
add(x, y, blockType, turnState);
newblock();
delline();
}
;
repaint();
}
// 是否合法的方法
public int blow(int x, int y, int blockType, int turnState) {
for (int a = 0; a < 4; a++) {
for (int b = 0; b < 4; b++) {
if (((shapes[blockType][turnState][a * 4 + b] == 1) && (map[x
+ b + 1][y + a] == 1))
|| ((shapes[blockType][turnState][a * 4 + b] == 1) && (map[x
+ b + 1][y + a] == 2))) {
return 0;
}
}
}
return 1;
}
// 消行的方法
public void delline() {
int c = 0;
for (int b = 0; b < 22; b++) {
for (int a = 0; a < 12; a++) {
if (map[a][b] == 1) {
c = c + 1;
if (c == 10) {
score += 10;
for (int d = b; d > 0; d--) {
for (int e = 0; e < 11; e++) {
map[e][d] = map[e][d - 1];
}
}
}
}
}
c = 0;
}
}
// 判断你挂的方法
public int gameover(int x, int y) {
if (blow(x, y, blockType, turnState) == 0) {
return 1;
}
return 0;
}
// 把当前添加map
public void add(int x, int y, int blockType, int turnState) {
int j = 0;
for (int a = 0; a < 4; a++) {
for (int b = 0; b < 4; b++) {
if (map[x + b + 1][y + a] == 0) {
map[x + b + 1][y + a] = shapes[blockType][turnState][j];
}
;
j++;
}
}
}
// 画方块的的方法
public void paintComponent(Graphics g) {
super.paintComponent(g);
// 画当前方块
for (j = 0; j < 16; j++) {
if (shapes[blockType][turnState][j] == 1) {
g.fillRect((j % 4 + x + 1) * 10, (j / 4 + y) * 10, 10, 10);
}
}
// 画已经固定的方块
for (j = 0; j < 22; j++) {
for (i = 0; i < 12; i++) {
if (map[i][j] == 1) {
g.fillRect(i * 10, j * 10, 10, 10);
}
if (map[i][j] == 2) {
g.drawRect(i * 10, j * 10, 10, 10);
}
}
}
g.drawString("score=" + score, 125, 10);
g.drawString("抵制不良游戏，", 125, 50);
g.drawString("拒绝盗版游戏。", 125, 70);
g.drawString("注意自我保护，", 125, 90);
g.drawString("谨防受骗上当。", 125, 110);
g.drawString("适度游戏益脑，", 125, 130);
g.drawString("沉迷游戏伤身。", 125, 150);
g.drawString("合理安排时间，", 125, 170);
g.drawString("享受健康生活。", 125, 190);
}
// 键盘监听
public void keyPressed(KeyEvent e) {
switch (e.getKeyCode()) {
case KeyEvent.VK_DOWN:
down();
break;
case KeyEvent.VK_UP:
turn();
break;
case KeyEvent.VK_RIGHT:
right();
break;
case KeyEvent.VK_LEFT:
left();
break;
}
}
// 无用
public void keyReleased(KeyEvent e) {
}
// 无用
public void keyTyped(KeyEvent e) {
}
// 定时器监听
class TimerListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
repaint();
if (blow(x, y + 1, blockType, turnState) == 1) {
y = y + 1;
delline();
}
;
if (blow(x, y + 1, blockType, turnState) == 0) {
if (flag == 1) {
add(x, y, blockType, turnState);
delline();
newblock();
flag = 0;
}
flag = 1;
}
;
}
}
}