Suitable for beginners to get started with Java programs

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Overview

JavaIt is ITone of the most popular programming languages ​​widely used in the industry. It is simple, robust, and helps us reuse code. In this article, let's look at some Javaapplications that understand the basics.

Getting started with Java programs

Computer program

Write a Javaprogram to perform basic calculator operations.

When you consider using a calculator, you will think of operations such as addition, subtraction, multiplication, and division. Let us use the following procedure to achieve basic calculator operations.

package com.niocoder;

import java.util.Scanner;

/**
 * Created by zhenglongfei on 2020/4/21
 *
 * @VERSION 1.0
 */
public class _01Calculator {
    public static void main(String[] args) {
        Scanner param = new Scanner(System.in);
        System.out.print("请输入第一个数字:");
        double first = param.nextDouble();
        System.out.print("请输入第二个数字:");
        double second = param.nextDouble();
        System.out.print("请输入运算符 (+, -, *, /): ");
        char operator = param.next().charAt(0);
        double result;
        //switch case for each of the operations
        switch (operator) {
            case '+':
                result = first + second;
                break;
            case '-':
                result = first - second;
                break;
            case '*':
                result = first * second;
                break;
            case '/':
                result = first / second;
                break;
            default:
                // operator doesn't match any case constant (+, -, *, /)default:
                System.out.println("Error! operator is not correct");
                return;
        }
        System.out.printf("%.1f %c %.1f = %.1f", first, operator, second, result);
    }
}

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When the above program is executed, the output is as follows:

请输入第一个数字:10
请输入第二个数字:10
请输入运算符 (+, -, *, /): +
10.0 + 10.0 = 20.0
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Use recursive factorial procedures

Write a Javaprogram to calculate the factorial of a number.

The factorial of a number is the product of all positive numbers less than or equal to the number. nThe factorial of is n！represented by . Now, let us write a program and use recursion to find the factorial of a number.

package com.niocoder;

import java.util.Scanner;

/**
 * Created by zhenglongfei on 2020/4/21
 *
 * @VERSION 1.0
 */
public class _02Factorial {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入一个数字:");
        //Stored the entered value in variable
        int num = scanner.nextInt();
        //Called the user defined function fact
        int factorial = fact(num);
        System.out.println("输入数字的阶乘是: " + factorial);
    }

    static int fact(int number) {
        if (number == 1) {
            return 1;
        }
        return number * fact(number - 1);
    }
}

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When executing the above program, you will get a factorial of a number as follows:

请输入一个数字:12
输入数字的阶乘是: 479001600
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Fibonacci sequence procedure

Write a Javaprogram to calculate the Fibonacci sequence up to na number.

It is a series, and the next item is the sum of the first two items. For example: 0 1 1 2 3 5 8 13 ... Let us write a Javaprogram to calculate the Fibonacci sequence.

package com.niocoder;

import java.util.Scanner;

/**
 * Created by zhenglongfei on 2020/4/21
 *
 * @VERSION 1.0
 */
public class _03Fibonacci {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入一个数字:");
        //Stored the entered value in variable
        int num = scanner.nextInt();
        int first = 0, second = 1;
        System.out.print(num + ":");
        while (first < num) {
            System.out.print(first + "+");
            int sum = first + second;
            first = second;
            second = sum;
        }
    }
}

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After executing the above code, the output is as follows:

请输入一个数字:100
100:0+1+1+2+3+5+8+13+21+34+55+89+
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Palindrome program

Write a Javaprogram to find out if a given string is a palindrome.

A palindrome is a number, string, or sequence, even if you reverse the order, they are the same. For example, RACECARif you spell backwards the RACECARsame as.

package com.niocoder;

import java.util.Scanner;

/**
 * Created by zhenglongfei on 2020/4/21
 *
 * @VERSION 1.0
 */
public class _04Palindrome {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("请输入一个字符串: ");
        String str = sc.nextLine();
        checkPalindrome(str);
    }

    private static void checkPalindrome(String str) {
        boolean flag = true;
        int length = str.length();
        for (int i = 0; i <= length / 2; i++) {
            if (str.charAt(i) != str.charAt(length - i - 1)) {
                flag = false;
                break;
            }
        }
        System.out.println(str + " 是否回文 = " + flag);
    }
}

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When running the code, it will check whether the given string is a palindrome, as shown below:

请输入一个字符串: abab
abab 是否回文 = false

请输入一个字符串: abba
abba 是否回文 = true
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Pattern program

JavaPrint a diamond pattern with a written program.

Here, the forloop is used to print the diamond pattern.

package com.niocoder;

import java.util.Scanner;

/**
 * Created by zhenglongfei on 2020/4/21
 *
 * @VERSION 1.0
 */
public class _05DiamondPattern {
    public static void main(String[] args) {
        int n, i, j, space = 1;
        System.out.print("请输入行数: ");
        Scanner s = new Scanner(System.in);
        n = s.nextInt();
        space = n - 1;
        for (j = 1; j <= n; j++) {
            for (i = 1; i <= space; i++) {
                System.out.print(" ");
            }
            space--;
            for (i = 1; i <= 2 * j - 1; i++) {
                System.out.print("*");
            }
            System.out.println("");
        }
        space = 1;
        for (j = 1; j <= n - 1; j++) {
            for (i = 1; i <= space; i++) {
                System.out.print(" ");
            }
            space++;
            for (i = 1; i <= 2 * (n - j) - 1; i++) {
                System.out.print("*");
            }
            System.out.println("");
        }
    }
}

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Output

请输入行数: 5
    *
   ***
  *****
 *******
*********
 *******
  *****
   ***
    *
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String reversal program

Write a Java program to reverse the letters in a given string.

This Javaprogram will reverse the letters in the string entered by the user. For example, " Hello People" will be called " olleH elpoeP". Let's use Javato achieve the same function.

package com.niocoder;

/**
 * Created by zhenglongfei on 2020/4/21
 *
 * @VERSION 1.0
 */
public class _06Stringreverse {
    public static void main(String[] args) {
        String str = "Welcome To niocoder";
        String[] strArray = str.split(" ");
        for (String temp : strArray) {
            System.out.println(temp);
        }
        for (int i = 0; i < 3; i++) {
            char[] s1 = strArray[i].toCharArray();
            for (int j = s1.length - 1; j >= 0; j--) {
                System.out.print(s1[j]);
            }
            System.out.print(" ");
        }
    }
}

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The output of the above program is as follows:

Welcome
To
niocoder
emocleW oT redocoin
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Mirror program

Write a Java program to check whether the given array is a mirrored array.

package com.niocoder;

/**
 * Created by zhenglongfei on 2020/4/21
 *
 * @VERSION 1.0
 */
public class _07MirrorInverse {

    public static void main(String[] args) {
        int arr[] = {3,4,2,0,1};
        if (isMirrorInverse(arr))
            System.out.println("Yes");
        else
            System.out.println("No");
    }

    static boolean isMirrorInverse(int arr[]) {
        for (int i = 0; i < arr.length; i++) {
            if (arr[arr[i]] != i)
                return false;
        }
        return true;
    }


}

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Output

Yes
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