title: error: bad operand types for binary operator '-'
body: <p>Here's my source code:</p>
  
  <pre><code>/* package whatever; // don't place package name! */
  
  import java.util.*;
  import java.lang.*;
  import java.io.*;
  
  /* Name of the class has to be "Main" only if the class is public. */
  class Ideone
  {
  public static void main (String[] args) throws java.lang.Exception
  {
      System.out.println( "Integer.MAX_VALUE = " +   Integer.MAX_VALUE );
      System.out.println( "Integer.MAX_VALUE + 1 = " +   (Integer.MAX_VALUE + 1) );
      System.out.println( "Integer.MAX_VALUE * 2 = " +  ( Integer.MAX_VALUE * 2) );
      System.out.println( "Integer.MAX_VALUE * 5 = " +  ( Integer.MAX_VALUE * 5) );
      System.out.println( "Integer.MAX_VALUE * 10 = " + (  Integer.MAX_VALUE * 10) );
      System.out.println( "Integer.MAX_VALUE = " +   Integer.MAX_VALUE );
      System.out.println( "Integer.MIN_VALUE - 1 = " +   (Integer.MIN_VALUE - 1) );
      System.out.println( "Integer.MIN_VALUE * 2 = " +  ( Integer.MIN_VALUE * 2) );
      System.out.println( "Integer.MIN_VALUE * 5 = " +  ( Integer.MIN_VALUE * 5) );
      System.out.println( "Integer.MIN_VALUE * 10 = " + (  Integer.MIN_VALUE * 10) );
      //Part 2
      System.out.println( "Integer.MAX_VALUE + 1.0 = " +   (Integer.MAX_VALUE + 1.0) );
      System.out.println( "Integer.MAX_VALUE * 2.0 = " +  ( Integer.MAX_VALUE * 2.0) );
      System.out.println( "Integer.MAX_VALUE * 5.0 = " +  ( Integer.MAX_VALUE * 5.0) );
      System.out.println( "Integer.MAX_VALUE * 10.0 = " + (  Integer.MAX_VALUE * 10.0) );
      System.out.println( "Integer.MIN_VALUE - 1.0 = " +   (Integer.MIN_VALUE - 1.0) );
      System.out.println( "Integer.MIN_VALUE * 2.0 = " +  ( Integer.MIN_VALUE * 2.0) );
      System.out.println( "Integer.MIN_VALUE * 5.0 = " +  ( Integer.MIN_VALUE * 5.0) );
      System.out.println( "Integer.MIN_VALUE * 10.0 = " + (  Integer.MIN_VALUE * 10.0) );
      //Part 3
      int a, b;
      a = 1;
      b = 2;
      System.out.println( "The ints a, b are " + a + ", " + b );
      System.out.println( "a + b is " + a + b );
      System.out.println( "a - b is " + a - b );
      System.out.println( "a * b is " + a * b );
      System.out.println( "a / b is " + a / b );
      //Part 4
      double aD, bD;
      aD = 1.0;
      bD = 2.0;
      System.out.println( "The doubles aD, bD are " + aD + ", " + bD  );
      System.out.println( "aD + bD is " + aD + bD );
      System.out.println( "aD - bD is "  + aD - bD );
      System.out.println( "aD * bD is " + aD * bD );
      System.out.println( "aD / bD is " + aD / bD );
  }
  }
  </code></pre>
  
  <p>Here's my error:</p>
  
  <pre><code>Compilation error   time: 0.1 memory: 320512 signal:0
  Main.java:37: error: bad operand types for binary operator '-'
      System.out.println( "a - b is " + a - b );
                                          ^
   first type:  String
   second type: int
  Main.java:46: error: bad operand types for binary operator '-'
      System.out.println( "aD - bD is "  +aD - bD );
                                             ^
  first type:  String
  second type: double
  2 errors
  </code></pre>
  
  <p>I am new to java and I am still figuring out arithmetic. I thought I was doing fine but I don't understand what's gone wrong. It is most probably a real rookie mistake but could you tell me what I did wrong?</p>