文章目录
java系列复习笔记（9）
第3部分第10章 java常用类库
1. StringBuffer类：
2. Runtime类：
- 代码演示：
package packageone;
public class DemoTest {
public static void main(String[] args) throws Exception{
Runtime runtime = Runtime.getRuntime() ;
String str = "" ;
for (int x=0;x<2000;x++){
str += x ;
}
System.out.println("MAX0="+runtime.maxMemory() );
System.out.println("TOTAL0="+runtime.totalMemory() );
System.out.println("FREE0="+runtime.freeMemory() );
runtime.gc();
System.out.println("MAX="+runtime.maxMemory() );
System.out.println("TOTAL0="+runtime.totalMemory() );
System.out.println("FREE0="+runtime.freeMemory() );
}
}
运行结果：
MAX0=3801088000
TOTAL0=257425408
FREE0=201053904
MAX=3801088000
TOTAL0=257425408
FREE0=255448992
3.System类：
4.数字操作类：
- 代码示例：36选7的彩票程序，最大值36，且不能有0或重复的数
package packageone;
import java.util.Random;
public class DemoRandom {
public static void main(String[] args) {
Random random = new Random() ;
int data[] = new int[7] ;
int foot = 0;
while(foot<7){
int t = random.nextInt(37) ;
if (!isRepeat(data,t)){
data[foot++] = t ;
}
}
java.util.Arrays.sort(data);
for (int i = 0;i<data.length;i++) {
System.out.print(data[i]+",");
}
}
private static boolean isRepeat(int[] data, int t) {
if (t == 0){
return true ;
}
for (int x=0 ;x<data.length;x++){
if (data[x]==t){
return true ;
}
}
return false;
}
}
运行结果：5,7,8,15,18,19,22,
5.日期处理类
package packageone;
import java.util.Date;
public class DemoDate {
public static void main(String[] args) {
Date date = new Date() ;
System.out.println(date) ;
long time = date.getTime();
System.out.println(time);
Date dt = new Date(time) ;
System.out.println(dt);
}
}
运行结果:
Sun Apr 10 17:29:02 CST 2022
1649582942657
Sun Apr 10 17:29:02 CST 2022
package packageone;
import java.text.SimpleDateFormat;
import java.util.Date;
public class DemoDate {
public static void main(String[] args) {
Date date = new Date() ;
System.out.println(date) ;
SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss") ;
String dateStr = sdf.format(date) ;
System.out.println(dateStr);
}
}
运行结果：
Sun Apr 10 17:42:25 CST 2022
2022年04月10日 17:42:25
6.比较器
package packageone;
import java.util.Arrays;
public class DemoArrays {
public static void main(String[] args) {
int[] data0 = new int[]{1,7,6,4,8,9,2,1,3,5,10};
java.util.Arrays.sort(data0);
System.out.println(Arrays.binarySearch(data0,6));
int data1[] = new int[5] ;
Arrays.fill(data1,6);
int data2[] = new int[]{6,6,6,6,6} ;
System.out.println(Arrays.toString(data0));
System.out.println(Arrays.toString(data1));
System.out.println(Arrays.toString(data2));
System.out.println(Arrays.equals(data1,data2));
}
}
package packageone;
import java.util.Arrays;
class Book implements Comparable<Book>{
private String name ;
private double price ;
public Book(String name,double price){
this.name = name ;
this.price = price ;
}
@Override
public String toString() {
return "Book{" +
"name='" + name + '\'' +
", price=" + price +
'}'+"\n";
}
@Override
public int compareTo(Book o) {
if (this.price>o.price){
return 1 ;
}else if(this.price<o.price){
return -1 ;
}else {
return 0;
}
}
}
public class ComparableSort {
public static void main(String[] args) {
Book books[] = new Book[] {
new Book("java开发",68.6),
new Book("javaWeb发",72.8),
new Book("ios开发",63.4),
new Book("c++开发",65.0),
new Book("Android开发",69.9)
};
Arrays.sort(books);
System.out.println(Arrays.toString(books));
}
}
运行结果：
[Book{name='ios开发', price=63.4}
, Book{name='c++开发', price=65.0}
, Book{name='java开发', price=68.6}
, Book{name='Android开发', price=69.9}
, Book{name='javaWeb发', price=72.8}
]
package packageone;
import java.util.Arrays;
import java.util.Comparator;
class BookDemo{
private String name ;
private double price ;
public BookDemo(String name,double price){
this.name = name ;
this.price = price ;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
@Override
public String toString() {
return "BookDemo{" +
"name='" + name + '\'' +
", price=" + price +
'}'+"\n";
}
}
class BookComparator implements Comparator<BookDemo>{
@Override
public int compare(BookDemo o1, BookDemo o2) {
if (o1.getPrice()>o2.getPrice()){
return 1 ;
}else if (o1.getPrice()<o2.getPrice()){
return -1 ;
}else {
return 0;
}
}
}
public class ComparatorTest {
public static void main(String[] args) {
BookDemo bookDemos[] = new BookDemo[] {
new BookDemo("java开发",68.6),
new BookDemo("javaWeb发",72.8),
new BookDemo("ios开发",63.4),
new BookDemo("c++开发",65.0),
new BookDemo("Android开发",69.9)
};
Arrays.sort(bookDemos,new BookComparator());
System.out.println(Arrays.toString(bookDemos));
}
}
7.正则表达式
package packageone;
public class ZhengzeBDS {
public static void main(String[] args) {
String took = "9524ytdgdv" ;
System.out.println(isNumber(took));
}
public static <len> boolean isNumber(String temp){
if (temp==null | "".equals(temp)){
return false ;
}
char data[] = temp.toCharArray() ;
for (int i = 0; i<data.length ;i++){
if (data[i]>'9' || data[i]<'0'){
return false ;
}
}
return true ;
}
}
public class ZhengzeBDS {
public static void main(String[] args) {
String took = "9524ytdgdv" ;
System.out.println(took.matches("\\d+"));
}
}
