JAVA 知识记录

发表于 2019-04-30 更新于 2019-05-20 分类于 JAVA 阅读次数：

再次复习一下JAVA知识，同时记录一下

JAVA中创建除主函数之外的函数 (在原先的class 或者另外创建class 都可行)

package ddd;
import java.io.*;
import java.io.BufferedInputStream;
import java.math.*;
import java.util.*;
public class Main
{
	public static void main( String[] args) {
		Scanner cin = new Scanner(System.in);
		int a,b;
		a = cin.nextInt();
		b = cin.nextInt();
		System.out.println(calculate.add(a, b));
		System.out.println(calculate.sub(a, b));
		System.out.println(mul(a,b));
	}
	public static int mul(int a,int b)
	{
		return a * b;
	}
}
class calculate {
	public static int add(int a,int b)
	{
		return a + b;
	}
	public static int sub(int a,int b)
	{
		return a - b;
	}
}

求出一个数除以另一个数的商以及余数。

public class Main
{
	public static void main( String[] args) {
		Scanner cin = new Scanner(System.in);
	    BigInteger a,b;
	    a = cin.nextBigInteger();
	    b = cin.nextBigInteger();
	    BigInteger result[] = a.divideAndRemainder(b);
	    System.out.println(result[0]);
	    System.out.println(result[1]);
	}
}

对字符串的修改。 String 本身是不可以修改的，但是可以通过转换为字符数组进行修改

public class Main
{
	public static void main( String[] args) {
		Scanner cin = new Scanner(System.in);
	    int i;
	    String s = "abcdefg";
	    System.out.println(s.charAt(0));
	    char [] ch;
	    ch = s.toCharArray();
	    for(i = 0; i < ch.length; ++i)
	    {
	    	ch[i] += 1;
	    }
	    System.out.println(ch);
	}
}

将int型强制转化为BigInteger类型以及 .compareTo 函数的使用

public class Main
{
	public static void main( String[] args) {
		Scanner cin = new Scanner(System.in);
	    int a = 10;
	    int b = 11;
	    BigInteger c ,d;
	    c = BigInteger.valueOf(a);
	    d = BigInteger.valueOf(b);
	    if(c.compareTo(d) == 0)
	    	System.out.println(1111);
	    else
	    	System.out.println(2222);
	}
}

JAVA 中的进制转换

//String st = Integer.toString(num, base);
//把num 当做10进制的数转成base进制的(base <= 35)
public class Main
{
	public static void main( String[] args) {
		Scanner cin = new Scanner(System.in);
		int num,base;
		num = cin.nextInt();
		base = cin.nextInt();
	    String st = Integer.toString(num,base);
	    System.out.println(st);
	}
}

// int num = Integer.parseInt(st, base); 
// 把 st 当做base进制 转成10进制的Int  与上面正好相反。
public class Main
{
	public static void main( String[] args) {
		Scanner cin = new Scanner(System.in);
		int num,base;
		String st = cin.nextLine();
		base = cin.nextInt();
		num = Integer.parseInt(st, base);
		System.out.println(num);
	}
}

//以某个进制读入，然后以某个进制输出。
public class Main
{
	public static void main( String[] args) {
		Scanner cin = new Scanner(System.in);
		BigInteger a;
		a = cin.nextBigInteger(2);
		String b;
		b = a.toString(10);
	    System.out.println(b);
		}
}

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