Automatic Conversion / Cast

[Thomas Markl]

Hello,
The automatic cast from float to int takes only place for first parameter.
Why not for the second, too?

class Test104
{
  public static void main( String[] args )
  {
    int x = 1 ;
    float y = 1.0F ; //Automatic Conversion float to int
    //Only takes place for SECOND Operator
    if ( x == y )
    {
      System.out.println( "Equal1" ) ;
    }
    
    float x0 = 1 ;
    int y0 = 1.0F ; //Why is this not possible for FIRST Operator
    if ( x0 == y0 )
    {
      System.out.println( "Equal0" ) ;
    }
  }
}

I get this error:

C:\Java\EigeneJavaProgramme>javac Test104.java 
Test104.java:7: possible loss of precision
found   : float
required: int
    float x0=1; int y0=1.0F; 
                       ^
1 error

Why?
Why don't I get the error before?
Thomas
[ edited to make code and error message more readable -ds ]
[ January 15, 2003: Message edited by: Dirk Schreckmann ]

[John Lee]

Originally posted by Thomas Markl:

Why don't I get the error before?

If I understand your question correctly, you are asking why:
float x = 1;
is ok.
int y = 1.0F
is not.
The reason is you can upcast implicitly. But when you want to downcast, your have to be explicitly.
So,
int y= (int)1.0F
will work.

[Layne Lund]

class Test104
{
  public static void main( String[] args )
  {
    int x = 1 ;
    float y = 1.0F ; //Automatic Conversion float to int

The above line doesn't do any automatic conversion. The variable y is declared as a float and the F indicates that the literal is a float, also.

    //Only takes place for SECOND Operator
    if ( x == y )

This comparison DOES have an automatic conversion. The variable x is converted to a float so that operation can occur. When an the orpands for an operator have different types, the larger (more bits) type is usually used.

    {
      System.out.println( "Equal1" ) ;
    }
    
    float x0 = 1 ;
    int y0 = 1.0F ; //Why is this not possible for FIRST Operator

Here you are trying to assign a float literal to an int variable. Since int uses less bits than float, the compiler will complain. There is no automatic conversion from int to float, only from float to int.

    if ( x0 == y0 )

If you can fix the above problem, this line will once again convert the int variable to a float.

    {
      System.out.println( "Equal0" ) ;
    }
  }
}

HTH
Layne

[Thomas Markl]

I think, now I got it:
Comparison of primitive numbers with „==“ and
Objects like Integer or String with „==“ and „equals“.

class Test104 {
  
    public static void main(String [] args) {
       int x=1; float y=1.0F; 
         //Comparison automatically casts smaller int
         //to bigger float!
         if(x==y) { System.out.println("Equal1");} 
       float x0=1; int y0=1; 
         //Comparison automatically casts smaller int
         //to bigger float!
         if(x0==y0) { System.out.println("Equal0");} 
       int x1=1; Integer y1= new Integer(1); 
         //intValue transfers Integer to int value
         if(x1==y1.intValue()) { System.out.println("Equal2");} 

       Integer x2=new Integer(1); Integer y2=new Integer(1);  
         if(x2.equals(y2)) { System.out.println("Equal3A");} 
         if(x2==y2){ System.out.println("Equal3");} 
          //To Compare objects with "==" they must be instances of
          //related classes otherwise "incomparable types error".
          Object o = new Object(); 
         if  (x2==o) {  System.out.println("Equal4A"); } 
          //Object and Integer are related by inheritance => "=="
          //compiles but as two objects => not equal. 
         if(x2.equals(y2)) { System.out.println("Equal3A");} 
       String x3="1"; String y3="1"; 
         if  (x3==y3) {  System.out.println("Equal4");}     
  }
}

C:\Java\EigeneJavaProgramme>java Test104
Equal1
Equal0
Equal2
Equal3A
Equal3A
Equal4

[Layne Lund]

Is this a new question? If so, what are you asking?
[ January 16, 2003: Message edited by: Layne Lund ]

[Dirk Schreckmann]

Note that the == operator doesn't compare obects. It compares object references. The expression ref1 == ref2 only returns true if ref1 and ref2 both refer to the exact same object.
Depending on how it's actually implemented, the equals method likely determines equality by considering the states of the objects in question.

[Robbie shi]

float x=1; it is ok
int x=1.0f; cant happen
Robbies
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