Java中T和?的区别

T和？的区别

@Test

public void testOne(){

// ?做对象的泛型来用

List list = findAllList( 1 );

list.forEach(temp ->{

System. out .print(temp);

});

System. out .println();

List lists = findAllList( 2 );

lists.forEach(temp ->{

System. out .print(temp);

});

//T做类的泛型，当输入的类型是One的时候，只能用One接

One one = new Class().newInstance();

//而不能用Two接

One one = new Class().newInstance();

}

class Two{

private Two(){

System. out .println( "Two" );

}

}

static class Class< T >{

T newInstance() {

return ( T ) new One();

}

}

private static class One{

private One(){

System. out .println( "One" );

}

}

private List findAllList(Integer type){

if (type == 1 ){

List list = new ArrayList<>();

list.add( 1 );

list.add( 2 );

return list;

} else {

List list = new ArrayList<>();

list.add( "AA" );

list.add( "BB" );

return list;

}

}