OLI 课程 & Java入学考试的五道题

Unit  1:: Programming with Java

✔️

机械、自动、不需要智慧地执行原始的内置指令。

字节码相同，JVM不同（体现平台）

✖️

In modern computers instructions can be stored and manipulated as other types of data. 对，都是位运算

We cannot describe an algorithm without a programming language.错，没有语言也可以写算法

compile：高级语言变成低级语言，设置一次就行，只翻译 不执行 很快，形成字节码。interpreter：要设置很多次，又翻译又执行。

z = x * y, 改y, z不变

用byte（带符号整数）存100。Although such data values can be stored in bigger numeric data types, e.g. short, int, or long, the most appropriate is byte as it takes least memory and has the range from -128 to 127.

double可以是也可以不是浮点型小数

打印前100个prime numbers

第一个x设为2，然后逐个往后试验

public static void main(String[] args)
{
    Scanner scan = new Scanner(System.in);

    int N = scan.nextInt();
    int x = 2;

    for(int i = 0; i <= N; i++)
    {
        int count = 0;

        for(int j = 1; j <= x; j++)
            if(x%j == 0)
                count++;

        if(count == 2)
            System.out.print(x + " ");

        x++;
    }
}

class driverFuction {
public static void main(String[] args)
{
Scanner scanner = new Scanner(System.in);
int x = 2;
int n = scanner.nextInt();

//count for n numbers
for(int i = 0; i <= n; i++) {
//reset count = 0;
int count = 0;

for (int j = 1; j <= x; j++) {
if (x % j == 0) count++;
}

if (count == 2) System.out.println("prime is x = " + x);

//add x
x++;
}
}
}

import java.util.Scanner;

public class ExArraySortElement
{
    public static void main(String[] args)
    {
        int n, temp;
        //scanner class object creation
        Scanner s = new Scanner(System.in);

        //input total number of elements to be read
        System.out.print("Enter the elements you want : ");
        n = s.nextInt();

        //integer array object
        int a[] = new int[n];

        //read elements
        System.out.println("Enter all the elements:");
        for (int i = 0; i < n; i++)
        {
            a[i] = s.nextInt();
//数组中的元素需要一个个地输入
        }

        //sorting elements
        for (int i = 0; i < n; i++)
        {
            for (int j = i + 1; j < n; j++)
            {
                if (a[i] > a[j])
                {
                    temp = a[i];
                    a[i] = a[j];
                    a[j] = temp;
                }
            }
        }

        //print sorted elements
        System.out.println("Ascending Order:");
        for (int i = 0; i < n ; i++)
        {
            System.out.println(a[i]);
        }
    }
}

// package whatever; // don't place package name!

import java.io.*;
import java.util.*;
import java.lang.*;

class driverFuction {
  public static void main(String[] args)
{
    Scanner scanner = new Scanner(System.in);
    int n = scanner.nextInt();

    //new an array
    int[] nums = new int[n];

    //input n numbers
    for (int i = 0; i < n; i++) {
      a[i] = scanner.nextInt();
    }

    //sort
    for (int i = 0; i < n; i++) {
      for (int j = i + 1; j < n; j++) {
        if (nums[i] > nums[j]) {
          int temp = nums[i];
          nums[i] = nums[j];
          nums[j] = temp;
        }
      }
    }

    //output
    for (int i = 0; i < n; i++) {
      System.out.println("nums[i] = " + nums[i]);
    }
}
}

https://www.includehelp.com/java-programs/sort-an-array-in-ascending-order.aspx

import java.util.Scanner;
class PrimeCheck
{
   public static void main(String args[])
   {
    int temp;
    boolean isPrime=true;
    Scanner scan= new Scanner(System.in);
    System.out.println("Enter any number:");
    //capture the input in an integer
    int num=scan.nextInt();
        scan.close();
    for(int i=2;i<=num/2;i++)
    {
           temp=num%i;
       if(temp==0)
       {
          isPrime=false;
          break;
       }
    }
    //If isPrime is true then the number is prime else not
    if(isPrime)
       System.out.println(num + " is a Prime Number");
    else
       System.out.println(num + " is not a Prime Number");
   }
}

https://beginnersbook.com/2014/01/java-program-to-check-prime-number/

// package whatever; // don't place package name!

import java.io.*;
import java.util.*;
import java.lang.*;

class Palindrome
{
public static void main(String args[])
{
Scanner in = new Scanner(System.in);

System.out.println("Enter a string to check if it is a palindrome");
String original = in.nextLine();

//int length = original.length();

String clean = original.replaceAll("\\s+", "").toLowerCase();

//单词里面有空格，要用replaceall
int length = clean.length();
int forward = 0;
int backward = length - 1;
while (backward > forward) {
char forwardChar = clean.charAt(forward++);
char backwardChar = clean.charAt(backward--);
if (forwardChar != backwardChar)
System.out.println("false");
}
System.out.println("true");
}
}

import java.io.*;
import java.util.*;
import java.lang.*;

class Palindrome
{
public static void main(String args[])
{
String word, File file;
int count = 0;
Scanner scanner = new Scanner(file);
while (scanner.hasNextLine()) {
String nextToken = scanner.next();//表示下一行
if (nextToken.equalsIgnoreCase(word))
count++;
}
return count;
}
}