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package com.sun.enterprise.management;
import java.util.Collection;
import java.util.Collections;
import java.util.Set;
import java.util.HashSet;
import java.io.Serializable;
import com.sun.appserv.management.util.misc.TypeCast;
/**
Demo of generic do/don't issues.
*/
public final class GenericsTest extends junit.framework.TestCase
{
public
GenericsTest()
{
}
private static class A implements Serializable
{
public static final long serialVersionUID = 999;
public A() {}
}
private static final class AA extends A
{
public static final long serialVersionUID = 9999;
public AA() {}
}
/**
commented out to avoid compiler warnings; code compiles and tests good,
and is useful in understanding generics.
// An example of an unchecked cast where the caller had better
// use the correct type of Set<T>; see testCallersProblem().
private <T extends Serializable> Set<T>
getSetOfSerializableT()
{
final Set<Serializable> result = new HashSet<Serializable>();
result.add( new String("hello") );
result.add( new Integer(0) );
result.add( new Boolean(false) );
// "warning: [unchecked] unchecked cast: found Set<String>, required Set<T>"
// it's up to the *caller* to ensure that T is a valid type as per javadoc
// or other semantics
return (Set<T>)result;
}
// Please see how getSetOfT_ImplCast() is implemented with a cast.
public void
test_getSetOfSerializableT()
{
final Set<String> s1 = getSetOfSerializableT(); // OK, no warning
final Set<Integer> s2 = getSetOfSerializableT(); // OK, no warning
final Set<Long> s3 = getSetOfSerializableT(); // OK, no warning
final Set<Serializable> s4 = getSetOfSerializableT(); // OK, no warning
// COMPILE FAILURE:
// final Set<Object> x = getSetOfT();
// final Set<?> x = getSetOfT();
TypeCast.checkSet( s4, Serializable.class);
try
{
TypeCast.checkSet( s1, String.class);
assert false;
}
catch( final ClassCastException e )
{
// should arrive here
}
try
{
TypeCast.checkSet( s2, Integer.class );
assert false;
}
catch( final ClassCastException e )
{
// should arrive here
}
try
{
TypeCast.checkSet( s3, Long.class );
assert false;
}
catch( final ClassCastException e )
{
// should arrive here
}
}
*/
/**
Method is "good"; no warnings.
*/
private Set<? extends Serializable>
getSetOfSerializableUnknown()
{
final Set<Serializable> result = new HashSet<Serializable>();
result.add( new String("hello") );
result.add( new Integer(0) );
result.add( new Boolean(false) );
return result;
}
/**
commented out to avoid compiler warnings; code compiles and tests good,
and is useful in understanding generics.
// Please see how getSetOfT_UnknownSubclass() is implemented.
public void
test_getSetOfSerializableSubclassUnknown()
{
// s1 is effectively read-only, since nothing can be put into it
final Set<? extends Serializable> s1 = getSetOfSerializableUnknown();
// warning: "unchecked cast"
final Set<Serializable> s2 = (Set<Serializable>)getSetOfSerializableUnknown();
}
*/
/**
Method is "good"; no warnings.
*/
private Set<Serializable>
getSetOfSerializable()
{
final Set<Serializable> result = new HashSet<Serializable>();
result.add( new String("hello") );
result.add( new Integer(0) );
result.add( new Boolean(false) );
return result;
}
/**
*/
public void
test_getSetOfSerializable()
{
// all OK. 's1' can contain any Serializable
final Set<Serializable> s1 = getSetOfSerializable();
TypeCast.checkSet( s1, Serializable.class );
// all OK, no warning.
final Set<? extends Serializable> s2 = getSetOfSerializable();
TypeCast.checkSet( s2, Serializable.class );
}
/*
private <T> void
checkValidItems( final Collection<T> c, final Class<T> theClass)
{
for( final T item : c )
{
if ( ! theClass.isAssignableFrom( item.getClass() ) )
{
throw new ClassCastException(
item.getClass() + " not assignable to " + theClass );
}
}
}
*/
public void
testAssign()
{
final Set<Serializable> serializableSet = new HashSet<Serializable>();
final Set<String> stringSet = new HashSet<String>();
// these of course must work; the types match
serializableSet.add( new Integer(0) );
serializableSet.add( new String() );
serializableSet.add( new Boolean(false) );
stringSet.add( "hello" );
serializableSet.addAll( stringSet );
// This is counterintuitive"; we just added all members of
// 'stringSet' to 'serializableSet', but we cannot assign the Set itself:
// Set<Serializable> illegal = stringSet;
// However, we can make this assignment if we use a wildcard Set,
// no further add() calls to the set can be made.
Set<? extends Serializable> unknownSub1 = null;
unknownSub1 = stringSet;
unknownSub1 = serializableSet;
}
public void
testCheckedSet()
{
final Set<Object> s = new HashSet<Object>();
TypeCast.checkSet( s, String.class );
TypeCast.checkSet( s, Integer.class );
s.add( "hello" );
TypeCast.checkSet( s, String.class );
TypeCast.checkSet( s, Object.class );
TypeCast.checkSet( s, Serializable.class );
try { TypeCast.checkSet( s, Integer.class ); assert false;}
catch( Exception e ) {/*good, expected*/}
final Set<String> ss = TypeCast.checkedStringSet( s );
try
{
// it's NOT a Set<Integer>, but let's verify that
// the exception is thrown.
final Set<Integer> x = TypeCast.asSet(ss);
x.add( new Integer(0) );
assert false;
}
catch( Exception e ) {/*good, expected*/}
final Set<String> sss = TypeCast.checkedStringSet( ss );
// assert( sss == ss ); bummer, it's not smart enough to not wrap it twice
final Set<Object> mixed = new HashSet<Object>();
mixed.add( "hello" );
mixed.add( new Integer(0) );
final Set<String> bogus = TypeCast.asSet(mixed);
final Set<String> checkedBogus = Collections.checkedSet( bogus, String.class );
// that worked. Our variant should reject it:
try
{
TypeCast.checkedStringSet( bogus );
}
catch( Exception e ) {/*good, expected*/}
}
}
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