面试题：
自动装箱:把基本数据类型会自动的变成其对应的包装类
自动拆箱:把包装类自动的变成其对象的基本数据类型
package Integer;
public class Demo {
public static void main(String[] args) {
Integer i = 10;
String binaryString = Integer.toBinaryString(i);
String hexString = Integer.toHexString(i);
String octalString = Integer.toOctalString(i);
System.out.println("二进制:" + binaryString + "\n十六进制:" + hexString + "\n八进制:" + octalString);
//4.将字符串类型的整数转成int类型的整数
//强类型语言:每种数据在java中都有各自的数据类型
//在计算的时候，如果不是同一种数据类型，是无法直接计算的。
//字符串已经转换成整数类型
int i1 = Integer.parseInt(binaryString);
System.out.println(i1);
//验证是否转换成功
System.out.println(i1 + 1);
//细节1:
//在类型转换的时候，括号中的参数只能是数字不能是其他，否则代码会报错
//细节2:
//8种包装类当中，除了character都有对应的parsexxx的方法，进行类型转换
String str ="true";
boolean b=Boolean.parseBoolean(str);
System.out.println(b);
}
}
package Integer;
import java.util.Scanner;
public class Demo1 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("请输入：");
String s = sc.nextLine();
//进行类型转换
int i = Integer.parseInt(s);
System.out.println(i);
//验证
System.out.println(i+1);
}
}
package execrise;
import javax.sound.sampled.SourceDataLine;
import java.util.ArrayList;
import java.util.Scanner;
public class Demo2 {
public static void main(String[] args) {
ArrayList<Integer> list = new ArrayList<>();
Scanner sc = new Scanner(System.in);
int sum = 0;
while (sum <= 200) {
System.out.println("请输入整数:");
String num1 = sc.nextLine();
int num = Integer.parseInt(num1);
if (num >= 1 && num <= 100) {
list.add(num);
sum += num;
} else {
System.out.print("输入有误,");
}
}
System.out.print("集合中的数据为：");
for (int i = 0; i < list.size(); i++) {
System.out.print(list.get(i) + " ");
}
}
}
方法1：
package execrise;
import java.util.Scanner;
public class Demo3 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
String s;
while (true) {
System.out.println("请输入字符串");
s = scanner.nextLine();
if (judement(s)) {
break;
} else {
System.out.print("输入错误,");
}
}
char[] array = s.toCharArray();
int number = 0;
for (int i = 0; i < array.length; i++) {
int i1 = array[i] - '0';
number = number * 10 + i1;
}
System.out.println("字符串转换后的数字为:" + number);
//验证
System.out.println(number + 1);
}
public static boolean judement(String string) {
char[] array = string.toCharArray();
for (int i = 0; i < array.length; i++) {
if (array[i] < '0' || array[i] > '9') {
return false;
}
}
if (string.length() < 1 || string.length() > 10) {
return false;
}
if (string.startsWith("0")) {
return false;
}
return true;
}
}
方法2：
package execrise;
import java.util.Scanner;
public class Demo4 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("请输入十进制整数:");
String s = scanner.nextLine();
int number = Integer.parseInt(s);
toBinary(number);
}
private static void toBinary(int number) {
String s = "";
while (number != 0) {
int yu = number % 2;
number = number / 2;
s = yu + s;
}
System.out.println("十进制对应二进制为:" + s);
}
}
JDK7:
package execrise;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class Demo5 {
public static void main(String[] args) throws ParseException {
Date date = new Date();
//System.out.println(System.currentTimeMillis());
String s = "2000-1-1";
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
Date parse = simpleDateFormat.parse(s);
long l = date.getTime() - parse.getTime();
System.out.println(l / 1000 / 60 / 60 / 24);
}
}
JDK8
package execrise;
import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;
public class Demo6 {
public static void main(String[] args) {
LocalDateTime now = LocalDateTime.now();
LocalDateTime localDateTime = LocalDateTime.of(1999, 2, 12, 4, 0, 0);
System.out.println(ChronoUnit.DAYS.between(localDateTime, now));
}
}
JDK7:
方法1：
package execrise;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class Demo7 {
public static void main(String[] args) throws ParseException {
String string1 = "2024-1-1";
String string2 = "2025-1-1";
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Date parse1 = sdf.parse(string1);
Date parse2 = sdf.parse(string2);
long l = parse2.getTime() - parse1.getTime();
if (l / (1000 * 60 * 60 * 24) == 365) {
System.out.println("不是闰年");
} else {
System.out.println("是闰年");
}
}
}
方法2：
JDK8：
方法1：
package execrise;
import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;
public class Demo8 {
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.of(2025, 1, 1, 0, 0);
LocalDateTime localDateTime1 = LocalDateTime.of(2024, 1, 1, 0, 0);
if (ChronoUnit.DAYS.between(localDateTime1, localDateTime) == 365) {
System.out.println("不是闰年");
} else {
System.out.println("是闰年");
}
}
}
方法2：
