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I am new to java, why a, b,c initialization are wrong in the following code.
public static void main(String[] args) {
if (args.length < 2)
throw new IllegalArgumentException ("we need 2 argumeents");
else {
int a = Integer.parseInt(args[0]);
int b = Integer.parseInt(args[1]);
int c = a+b;
}
System.out.println(a + " + " + b + " = " + c);
}
Java works differently compared to JavaScript. Every {} block has an own variable scope. Variables defined inside a block are not visible outside.
public static void main(String[] args) {
{
int x=1;
System.out.println(x); // prints 1
}
{
int x=2;
System.out.println(x); // prints 2
}
// System.out.println(x); // error: cannot find symbol
}
Related
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I'm just having a practise at some java coding and was wondering if there was a way to use a String if else statement to change change an integer, as the following doesn't like the c = a * b
int a, b, c;
Scanner sc = new Scanner(System.in);
System.out.println("Enter first number");
a = sc.nextInt();
System.out.println("Enter * + - or / ");
String d = sc.nextLine();
System.out.println("Enter second number");
b = sc.nextInt();
if (d.equals("*")){
c = a * b;
}
System.out.println(a + " " + d + " b " + " = " + c);
This happens because the variable "c" is initialized only if the conditional if (d.equals("*")) {...} is true, to solve this you have two options:
Just initialize "c" :
int a, b, c = 0;
or add else statement
if (d.equals("*")){
c = a * b;
}else {
c = 0;
}
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Write a Java program with a recursive method that accepts a value i as input and computes the sum:
m(i) = 1/3 + 2/5 + 3/7 + 4/9 + 5/11 + ... + i/(2i + 1)
So far I have:
import java.util.Scanner;
public class Recursion {
public static void main(String[] args) {
Scanner sc= new Scanner(System.in);
System.out.println("Enter an i: ");
int i = sc.nextInt();
if (i == 0) {
System.out.println(0);
}
else {
System.out.println(i / (2 * i + 1) + (main(i-1)));
}
}
}
The code isn't compiling. Please help!!
Ok I think I finally understand what you're trying to do! The problem is you're actually trying to build a string! The method is doing what it should, your return just isn't really doing what it should.
import java.util.Scanner;
public class Recursion
{
private static String result = null;
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter an i: ");
int i = sc.nextInt();
System.out.println(recursion(i));
}
public static String recursion(int i)
{
if(i != 0)
{
if(result == null)
{
result = (i + "/" + (2 * i + 1));
recursion(i - 1);
}
else
{
result = result.concat(" + ").concat(i + "/" + (2 * i + 1));
recursion(i - 1);
}
}
return result;
}
}
Please let me know if this does what you want it to!
You shouldn't use recursion on the main function. Just create a second function that isn't the main and it should work:
import java.util.Scanner;
public class Recursion {
public static void main(String[] args) {
Scanner sc= new Scanner(System.in);
System.out.println("Enter an i: ");
int i = sc.nextInt();
System.out.println(recursion(i));
}
public int recursion(int i){
if (i == 0) {
return 0;
}
else {
return (i / (2 * i + 1) + (recursion(i-1)));
}
}
}
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I made this program on C,and I have no idea of Java (new-yοung developer).Can you help me to "translate" it on Java?
#include<stdio.h>
#include<stdlib.h>
#include<graphics.h>
void printbin(int num)
{
int binnum;
binnum=num%2;
num=num/2;
if (num!=0) printbin(num);
printf("%d",binnum);
return;
system("pause");
}
int main(void)
{
int posnumber,binnum;
printf("Give a number : ");
scanf("%d",&posnumber);
printbin(posnumber);
printf("\n");
return 0;
}
You can learn from this code, hope this can help you:
//here is comments in java
package help;
import java.util.Scanner;
//this is the way how you can all the libraries in java so
/*
#include<stdio.h>
#include<stdlib.h>
#include<graphics.h>
*/
//here name of your class
public class Help {
//here name of your methode
public static void printbin(int num) {
int binnum;
binnum = num % 2;
num = num / 2;
if (num != 0) {
printbin(num);
}
System.out.println(binnum);
}
//here is the main methode in java
public static void main(String args[]) {
int posnumber, binnum;
Scanner scan = new Scanner(System.in);
System.out.println("Give a number : ");
posnumber = scan.nextInt();
System.out.println(posnumber);
}
}
Good luck, and good start with java :)
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I'm writing a program to find out if a number is even or odd and I have all of the code working, but I don't know how to write in other examples. Here is the code I have so far:
import static java.lang.System.*;
public class numberverify
{
public static boolean isOdd( int num)
{
return ((num % 2) == 1);
}
public static boolean isEven( int num)
{
return ((num % 2) == 0);
}
}
and the runner:
import static java.lang.System.*;
import java.util.Scanner;
public class numberverifyrunner
{
public static void main ( String[] args )
{
Scanner keyboard = new Scanner(in);
System.out.print("Enter an Integer :: ");
int num = keyboard.nextInt();
System.out.println( num + " is odd :: " + numberverify.isOdd(num));
System.out.println( num + " is even :: " + numberverify.isEven(num) + "\n");
//add in more test cases
}
}
Do this:
while(keyboard.hasNextInt())
{
int num = keyboard.nextInt();
System.out.println( num + " is odd :: " + numberverify.isOdd(num));
System.out.println( num + " is even :: " + numberverify.isEven(num) + "\n");
}
The program should quit if you put anything other than an integer in.
You could simplify this code somewhat (and make it easier to maintain) by only having a single method that performs the check. The second method can simply call the first one, for example:
public static boolean isOdd(int num) {
return ((num % 2) == 1);
}
public static boolean isEven(int num) {
return !isOdd(num);
}
For that matter, using a bitwise AND operation here is more efficient:
public status boolean isEven(int num) {
return (num & 1) == 0;
}
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I want to have a string variable showing next to my int variable but it doesn't seem to work.
public class ThreeLittleNumbers {
public static void main(String[] argts) {
String as = "Number 1: ";
String bs = "Number 2: ";
String cs = "Number 3: ";
int a = 1;
int b = 3;
int c = 5;
String tot = "Total: ";
System.out.println(as+a);
System.out.println(bs+b);
System.out.println(cs+c);
System.out.println(tot);
System.out.print(a+b+c);
}
}
If I understand your question, then this
System.out.println(tot);
System.out.print(a + b + c);
should be
System.out.print(tot);
System.out.println(a + b + c);
When I make the change above, I get output like you seem to be asking for -
Number 1: 1
Number 2: 3
Number 3: 5
Total: 9
Another option would be to use printf and something like
System.out.printf("%s %d%n", tot, a + b + c);