有人知道如何将参数与对象进行比较吗？我一直在尝试按照此处最后一个问题中给出的说明进行操作：http: //prntscr.com/1zaq0y但是，似乎没有问题。
public class Classification
{
String changes;
String rating;
String description;
Classification()
{
rating = "G";
description = "Suitable for general audiences";
}
Classification(String must)
{
if(must != "G" || must!= "PG" || must!="M")
{
throw new NullPointerException ("Not equal");
}
rating = must;
if(rating == "G")
{
description = "Suitable for general audiences";
}
if(rating == "PG")
{
description = "Parental guidance recommended";
}
if(rating == "M")
{
description = "Suitable for mature audiences";
}
}
Classification (int num, String para)
{
if(num!= 13 || num!= 15 || num!=16 || num!=18)
{
throw new IllegalArgumentException("Not equal");
}
if(para==null)
{
throw new NullPointerException("String is null");
}
if(num == 16)
{
rating = "R";
description = para;
}
changes = rating + num;
}
void printClassification()
{
print("Rated " + rating + ": " + description);
}
void derestrict()
{
if(rating == "M")
{
rating = "PG";
}
if(rating == "PG")
{
rating = "G";
}
if(rating == "G")
{
throw new IllegalArgumentException("G is least restrictive");
}
if(changes == "R18")
{
changes = "R16";
}
if(changes == "R15")
{
changes = "R13";
}
}
Classification isLessRestrictive(Classification compare)
{
if(compare==null)
{
throw new NullPointerException ("Classification para is null");
}
if(changes<compare)
{
return true;
}
return false;
}
}