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java自动排序函数.......
要实现排序功能,一般有两种途径,这里对基本类型不适用,基本类型一般有Arrays中的静态方法.
- 对象本身实现Comparable接口,那么该类的实例就是可以排序的. 有关Comparable: 只要实现了Comparable接口,就可以调用Collections的sort方法对集合中的元素排序.
- 指定一个Comparator,也就是实现了Comparator的类的一个实例. 但是Java本身只提供了一个Comparator的实现,就是Collections.reverseOrder(). 该方法返回的是一个已经实现了Comparable接口的反序. 看一下Comparator的全部内容:
public interface Comparator {
int compare(Object o1, Object o2);
boolean equals(Object obj);
}
定义了两个方法,其实我们一般都只需要实现compare方法就行了,因为类都是默认从Object继承,所以会使用Object的equals方法. Comparator一般都作为一个匿名类出现,对于没有实现Comparable的对象的集合,排序的时候需要指定一个Comparator. 这里举例说明 对于实现了Comparable的类我们就用最简单的Integer
List list = new ArrayList();
list.add(new Integer(3));
list.add(new Integer(53));
list.add(new Integer(34));
Collections.sort(list);
对于没有实现Comparable的,我们就用Object,按照hashCode大小来排序.
List list = new ArrayList();
list.add(new Object());
list.add(new Object());
list.add(new Object());
Collections.sort(list, new Comparator() {
public int compare(Object o1, Object o2) {
return (o1.hashCode() - o2.hashCode());
}
});
如何在Java中从键盘输入10个数,用选择法按降序排序并输出？
在Java中在数组中保存10个数,调用下面的排序函数，用选择法按降序排序：
public static void selectionSort(int[] arr) {
for (int i = 0; i < arr.length - 1; i++) {
int max = i;
for (int j = i + 1; j < arr.length; j++) {
if (arr[max] < arr[j]) {
max = j;
}
}
if (max != i) {
int tmp = arr[max];
arr[max] = arr[i];
arr[i] = tmp;
}
}
}
java定制排序
文件名：Frame1.java 关键代码：
//选择排序法函数
public void select_Sort(int[] num) {
int i, j, MX;
int temp;
for (i = 0; i < num.length - 1; i++) {
MX = i;
for (j = i + 1; j < num.length; j++) {
if (num[MX] < num[j]) {
MX = j;
}
}
temp = num[i];
num[i] = num[MX];
num[MX] = temp;
}
}
//插入排序函数
public void insert_Sort(int[] data) {
int i, j, mx;
int key;
for (i = 1; i < data.length - 1; i++) {
key = data[i];
mx = i;
for (j = i - 1; j > 0; j--) {
if (key < data[j]) {
data[j + 1] = data[j];
mx = j;
}
}
data[mx] = key;
}
}
全部代码
package mytest;
import java.awt.BorderLayout;
import java.awt.Dimension;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JLabel;
import java.awt.Rectangle;
import javax.swing.JTextField;
import javax.swing.JButton;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyAdapter;
import javax.swing.JOptionPane;
public class Frame1 extends JFrame {
JPanel contentPane;
JLabel jLabel1 = new JLabel();
JLabel jLabel2 = new JLabel();
JLabel jLabel3 = new JLabel();
JLabel jLabel4 = new JLabel();
JTextField txt1 = new JTextField();
JTextField txtOrder = new JTextField();
JButton btn2 = new JButton();
JTextField txt2 = new JTextField();
JTextField txtIn = new JTextField();
JButton btn1 = new JButton();
public Frame1() {
try {
setDefaultCloseOperation(EXIT_ON_CLOSE);
jbInit();
} catch (Exception exception) {
exception.printStackTrace();
}
}
private void jbInit() throws Exception {
contentPane = (JPanel) getContentPane();
contentPane.setLayout(null);
setSize(new Dimension(457, 432));
setTitle("Frame Title");
jLabel1.setText("排序前");
jLabel1.setBounds(new Rectangle(30, 99, 59, 36));
jLabel2.setText("排序后（1）");
jLabel2.setBounds(new Rectangle(27, 183, 66, 36));
jLabel3.setText("排序后（2）");
jLabel3.setBounds(new Rectangle(29, 259, 76, 36));
jLabel4.setText("用户输入");
jLabel4.setBounds(new Rectangle(28, 35, 71, 36));
txt1.setBounds(new Rectangle(116, 182, 307, 33));
txtOrder.setBounds(new Rectangle(118, 106, 307, 37));
btn2.setBounds(new Rectangle(263, 327, 162, 42));
btn2.setText("插入排序");
btn2.addActionListener(new Frame1_btn2_actionAdapter(this));
txt2.setBounds(new Rectangle(118, 259, 307, 33));
txtIn.setText("请输入数字，并按回车键。一次只能输入一个数字");
txtIn.setBounds(new Rectangle(116, 37, 306, 39));
txtIn.addKeyListener(new Frame1_txtIn_keyAdapter(this));
btn1.setBounds(new Rectangle(28, 327, 162, 42));
btn1.setText("选择排序");
btn1.addActionListener(new Frame1_btn1_actionAdapter(this));
contentPane.add(jLabel4);
contentPane.add(jLabel1);
contentPane.add(txtOrder);
contentPane.add(jLabel2);
contentPane.add(txt1);
contentPane.add(jLabel3);
contentPane.add(txt2);
contentPane.add(txtIn);
contentPane.add(btn1);
contentPane.add(btn2);
}
int[] Number1 = new int[10];
int[] Number2 = new int[10];
int i = 0;
public void txtIn_keyPressed(KeyEvent e) {
try {
if (e.getKeyChar() == '\n') {
Number1[i] = Integer.parseInt(txtIn.getText().trim());
Number2[i] = Integer.parseInt(txtIn.getText().trim());
String txt = txtOrder.getText().trim();
txtOrder.setText(txt + txtIn.getText().trim() + ",");
txtIn.setText("");
txtIn.requestFocus(true);
if (++i < 10) {
JOptionPane.showMessageDialog(this, "只能输入10个整数!");
txtIn.setText("");
return;
}
}
} catch (Exception ex) {
JOptionPane.showMessageDialog(this, ex.getMessage());
txtIn.setText("");
ex.printStackTrace();
}
}
//选择排序法函数
public void select_Sort(int[] num) {
int i, j, MX;
int temp;
for (i = 0; i < num.length - 1; i++) {
MX = i;
for (j = i + 1; j < num.length; j++) {
if (num[MX] < num[j]) {
MX = j;
}
}
temp = num[i];
num[i] = num[MX];
num[MX] = temp;
}
}
//选择排序按钮监听方法
public void btn1_actionPerformed(ActionEvent e) {
txt1.setText("");
select_Sort(Number1); //调用选择排序函数
for (int j = 0; j < Number1.length; j++) {
String txt = txt1.getText().trim();
txt1.setText(txt + Number1[j] + ",");
}
}
//插入排序函数
public void insert_Sort(int[] data) {
int i, j, mx;
int key;
for (i = 1; i < data.length - 1; i++) {
key = data[i];
mx = i;
for (j = i - 1; j > 0; j--) {
if (key < data[j]) {
data[j + 1] = data[j];
mx = j;
}
}
data[mx] = key;
}
}
public void btn2_actionPerformed(ActionEvent e) {
txt2.setText("");
insert_Sort(Number2);
for (int j = 0; j < Number2.length; j++) {
String txt = txt2.getText().trim();
txt2.setText(txt + Number2[j] + ",");
}
}
//主函数
public static void main(String[] arges) {
Frame1 F = new Frame1();
F.setVisible(true);
}
}
class Frame1_btn2_actionAdapter implements ActionListener {
private Frame1 adaptee;
Frame1_btn2_actionAdapter(Frame1 adaptee) {
this.adaptee = adaptee;
}
public void actionPerformed(ActionEvent e) {
adaptee.btn2_actionPerformed(e);
}
}
class Frame1_btn1_actionAdapter implements ActionListener {
private Frame1 adaptee;
Frame1_btn1_actionAdapter(Frame1 adaptee) {
this.adaptee = adaptee;
}
public void actionPerformed(ActionEvent e) {
adaptee.btn1_actionPerformed(e);
}
}
class Frame1_txtIn_keyAdapter extends KeyAdapter {
private Frame1 adaptee;
Frame1_txtIn_keyAdapter(Frame1 adaptee) {
this.adaptee = adaptee;
}
public void keyPressed(KeyEvent e) {
adaptee.txtIn_keyPressed(e);
}
}
java常用函数方法
Java的一些常用函数,方法总结：
- 数组方面: 数组是一个对象,数组名可以理解和C++里面一样,
System.arraycopy(src, srcindex, dst, dstindex, src.length);java.util.Arrays.sort(数组名);//块数排序法进行排序java.util.Arrays.binarySearch(arr, key);//从哪里收,关键值,返回索引.没有的话返回-1java.util.Arrays.fill(arr, value);//设置数组初始值Array.equals(arr1, arr2)//比较两个数组中元素是不是全部相等,是返回true,不是返回false- 时间方面:
public static String dateToStr(java.util.Date date) {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String str = sdf.format(date);
return str;
}
import java.text.SimpleDateFormat;
import java.util.Calendar;
public class DateUtil {
public static java.util.Date parseDate(String dateStr, String format) {
java.util.Date date = null;
try {
java.text.DateFormat df = new java.text.SimpleDateFormat(format);
String dt = dateStr.replaceAll("-", "/");
if ((!dt.equals("")) && (dt.length() < format.length())) {
dt += format.substring(dt.length()).replaceAll("[YyMmDdHhSs]", "0");
}
date = (java.util.Date) df.parse(dt);
} catch (Exception e) {
}
return date;
}
public static java.util.Date parseDate(String dateStr) {
return parseDate(dateStr, "yyyy/MM/dd");
}
public static String format(java.util.Date date, String format) {
String result = "";
try {
if (date != null) {
java.text.DateFormat df = new java.text.SimpleDateFormat(format);
result = df.format(date);
}
} catch (Exception e) {
}
return result;
}
public static String format(java.util.Date date) {
return format(date, "yyyy/MM/dd");
}
public static int getYear(java.util.Date date) {
java.util.Calendar c = java.util.Calendar.getInstance();
c.setTime(date);
return c.get(java.util.Calendar.YEAR);
}
public static int getMonth(java.util.Date date) {
java.util.Calendar c = java.util.Calendar.getInstance();
c.setTime(date);
return c.get(java.util.Calendar.MONTH) + 1;
}
public static int getDay(java.util.Date date) {
java.util.Calendar c = java.util.Calendar.getInstance();
c.setTime(date);
return c.get(java.util.Calendar.DAY_OF_MONTH);
}
public static int getHour(java.util.Date date) {
java.util.Calendar c = java.util.Calendar.getInstance();
c.setTime(date);
return c.get(java.util.Calendar.HOUR_OF_DAY);
}
public static int getMinute(java.util.Date date) {
java.util.Calendar c = java.util.Calendar.getInstance();
c.setTime(date);
return c.get(java.util.Calendar.MINUTE);
}
public static int getSecond(java.util.Date date) {
java.util.Calendar c = java.util.Calendar.getInstance();
c.setTime(date);
return c.get(java.util.Calendar.SECOND);
}
public static long getMillis(java.util.Date date) {
java.util.Calendar c = java.util.Calendar.getInstance();
c.setTime(date);
return c.getTimeInMillis();
}
public static String getDate(java.util.Date date) {
return format(date, "yyyy/MM/dd");
}
public static String getTime(java.util.Date date) {
return format(date, "HH:mm:ss");
}
public static String getDateTime(java.util.Date date) {
return format(date, "yyyy/MM/dd HH:mm:ss");
}
public static java.util.Date addDate(java.util.Date date, int day) {
java.util.Calendar c = java.util.Calendar.getInstance();
c.setTimeInMillis(getMillis(date) + ((long) day) * 24 * 3600 * 1000);
return c.getTime();
}
public static int diffDate(java.util.Date date, java.util.Date date1) {
return (int) ((getMillis(date) - getMillis(date1)) / (24 * 3600 * 1000));
}
public static String getMonthBegin(String strdate) {
java.util.Date date = parseDate(strdate);
return format(date, "yyyy-MM") + "-01";
}
public static String getMonthEnd(String strdate) {
java.util.Date date = parseDate(getMonthBegin(strdate));
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.add(Calendar.MONTH, 1);
calendar.add(Calendar.DAY_OF_YEAR, -1);
return formatDate(calendar.getTime());
}
public static String formatDate(java.util.Date date) {
return formatDateByFormat(date, "yyyy-MM-dd");
}
public static String formatDateByFormat(java.util.Date date, String format) {
String result = "";
if (date != null) {
try {
SimpleDateFormat sdf = new SimpleDateFormat(format);
result = sdf.format(date);
} catch (Exception ex) {
ex.printStackTrace();
}
}
return result;
}
}
Java日期格式化及其使用例子
- SimpleDateFormat担当重任,怎样格式化都行
import java.util.Date;
import java.text.SimpleDateFormat;
public class Demo {
public static void main(String[] args) {
Date now = new Date();
SimpleDateFormat f = new SimpleDateFormat("今天是" + "yyyy年MM月dd日 E kk点mm分");
System.out.println(f.format(now));
f = new SimpleDateFormat("a hh点mm分ss秒");
System.out.println(f.format(now));
}
}
- 从字符串到日期类型的转换：
import java.util.Date;
import java.text.SimpleDateFormat;
import java.util.GregorianCalendar;
import java.text.*;
public class Demo {
public static void main(String[] args) {
String strDate = "2005年04月22日";
//注意：SimpleDateFormat构造函数的样式与strDate的样式必须相符
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy年MM月dd日");
//必须捕获异常
try {
Date date = simpleDateFormat.parse(strDate);
System.out.println(date);
} catch (ParseException px) {
px.printStackTrace();
}
}
}
- 将毫秒数换转成日期类型
import java.util.Date;
import java.text.SimpleDateFormat;
import java.util.GregorianCalendar;
import java.text.*;
public class Demo {
public static void main(String[] args) {
long now = System.currentTimeMillis();
System.out.println("毫秒数：" + now);
Date dNow = new Date(now);
System.out.println("日期类型：" + dNow);
}
}
- 获取系统时期和时间，转换成SQL格式后更新到数据库
java.util.Date d = new java.util.Date(); //获取当前系统的时间
//格式化日期
new java.text.SimpleDateFormat s = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateStr = s.format(d); //转为字符串
//使用RS更新数据库，仍然要用rs.updateString，而不是rs.updateDade。
rs.updateString("regtime", dateStr); //regtime字段为datetime类型的
- 按本地时区输出当前日期
Date myDate = new Date();
System.out.println(myDate.toLocaleString());
输出结果为：
2003-5-30
- 如何格式化小数
DecimalFormat df = new DecimalFormat(",###.00");
double aNumber = 33665448856.6568975;
String result = df.format(aNumber);
System.out.println(result);
输出结果为：
33,665,448,856.66
其他：获取毫秒时间 System.currentTimeMillis();
7. 在数据库里的日期只以年-月-日的方式输出
定义日期格式：SimpleDateFormat sdf = new SimpleDateFormat("yy-MM-dd");
SQL语句为：
String sqlStr = "select bookDate from roomBook where bookDate between '2007-4-10' and '2007-4-25'";
输出：
System.out.println(df.format(rs.getDate("bookDate")));
