在Java中，这些区别是什么:
Object o1 = ....
o1.getClass().getSimpleName();
o1.getClass().getName();
o1.getClass().getCanonicalName();
我已经检查了Javadoc多次，但这从未很好地解释它。 我还运行了一个测试，并没有反映出调用这些方法背后的任何真正意义。
当前回答
如果您对某些事情不确定，请先尝试编写一个测试。
我是这样做的:
class ClassNameTest {
public static void main(final String... arguments) {
printNamesForClass(
int.class,
"int.class (primitive)");
printNamesForClass(
String.class,
"String.class (ordinary class)");
printNamesForClass(
java.util.HashMap.SimpleEntry.class,
"java.util.HashMap.SimpleEntry.class (nested class)");
printNamesForClass(
new java.io.Serializable(){}.getClass(),
"new java.io.Serializable(){}.getClass() (anonymous inner class)");
}
private static void printNamesForClass(final Class<?> clazz, final String label) {
System.out.println(label + ":");
System.out.println(" getName(): " + clazz.getName());
System.out.println(" getCanonicalName(): " + clazz.getCanonicalName());
System.out.println(" getSimpleName(): " + clazz.getSimpleName());
System.out.println(" getTypeName(): " + clazz.getTypeName()); // added in Java 8
System.out.println();
}
}
打印:
int.class (primitive):
getName(): int
getCanonicalName(): int
getSimpleName(): int
getTypeName(): int
String.class (ordinary class):
getName(): java.lang.String
getCanonicalName(): java.lang.String
getSimpleName(): String
getTypeName(): java.lang.String
java.util.HashMap.SimpleEntry.class (nested class):
getName(): java.util.AbstractMap$SimpleEntry
getCanonicalName(): java.util.AbstractMap.SimpleEntry
getSimpleName(): SimpleEntry
getTypeName(): java.util.AbstractMap$SimpleEntry
new java.io.Serializable(){}.getClass() (anonymous inner class):
getName(): ClassNameTest$1
getCanonicalName(): null
getSimpleName():
getTypeName(): ClassNameTest$1
在最后一个块中有一个空条目，其中getSimpleName返回一个空字符串。
这样做的结果是:
the name is the name that you'd use to dynamically load the class with, for example, a call to Class.forName with the default ClassLoader. Within the scope of a certain ClassLoader, all classes have unique names. the canonical name is the name that would be used in an import statement. It might be useful during toString or logging operations. When the javac compiler has complete view of a classpath, it enforces uniqueness of canonical names within it by clashing fully qualified class and package names at compile time. However JVMs must accept such name clashes, and thus canonical names do not uniquely identify classes within a ClassLoader. (In hindsight, a better name for this getter would have been getJavaName; but this method dates from a time when the JVM was used solely to run Java programs.) the simple name loosely identifies the class, again might be useful during toString or logging operations but is not guaranteed to be unique. the type name returns "an informative string for the name of this type", "It's like toString: it's purely informative and has no contract value". (as written by sir4ur0n)
你也可以参考Java语言规范文档来了解这些类型的Java API技术细节:
下面是关于这个主题的Java 11规范:https://docs.oracle.com/javase/specs/jls/se11/html/jls-6.html#jls-6.7 例6.7 - 2。例6.7-2。分别讨论了完全限定名称和完全限定名称v.规范名称
其他回答
如果您对某些事情不确定，请先尝试编写一个测试。
我是这样做的:
class ClassNameTest {
public static void main(final String... arguments) {
printNamesForClass(
int.class,
"int.class (primitive)");
printNamesForClass(
String.class,
"String.class (ordinary class)");
printNamesForClass(
java.util.HashMap.SimpleEntry.class,
"java.util.HashMap.SimpleEntry.class (nested class)");
printNamesForClass(
new java.io.Serializable(){}.getClass(),
"new java.io.Serializable(){}.getClass() (anonymous inner class)");
}
private static void printNamesForClass(final Class<?> clazz, final String label) {
System.out.println(label + ":");
System.out.println(" getName(): " + clazz.getName());
System.out.println(" getCanonicalName(): " + clazz.getCanonicalName());
System.out.println(" getSimpleName(): " + clazz.getSimpleName());
System.out.println(" getTypeName(): " + clazz.getTypeName()); // added in Java 8
System.out.println();
}
}
打印:
int.class (primitive):
getName(): int
getCanonicalName(): int
getSimpleName(): int
getTypeName(): int
String.class (ordinary class):
getName(): java.lang.String
getCanonicalName(): java.lang.String
getSimpleName(): String
getTypeName(): java.lang.String
java.util.HashMap.SimpleEntry.class (nested class):
getName(): java.util.AbstractMap$SimpleEntry
getCanonicalName(): java.util.AbstractMap.SimpleEntry
getSimpleName(): SimpleEntry
getTypeName(): java.util.AbstractMap$SimpleEntry
new java.io.Serializable(){}.getClass() (anonymous inner class):
getName(): ClassNameTest$1
getCanonicalName(): null
getSimpleName():
getTypeName(): ClassNameTest$1
在最后一个块中有一个空条目，其中getSimpleName返回一个空字符串。
这样做的结果是:
the name is the name that you'd use to dynamically load the class with, for example, a call to Class.forName with the default ClassLoader. Within the scope of a certain ClassLoader, all classes have unique names. the canonical name is the name that would be used in an import statement. It might be useful during toString or logging operations. When the javac compiler has complete view of a classpath, it enforces uniqueness of canonical names within it by clashing fully qualified class and package names at compile time. However JVMs must accept such name clashes, and thus canonical names do not uniquely identify classes within a ClassLoader. (In hindsight, a better name for this getter would have been getJavaName; but this method dates from a time when the JVM was used solely to run Java programs.) the simple name loosely identifies the class, again might be useful during toString or logging operations but is not guaranteed to be unique. the type name returns "an informative string for the name of this type", "It's like toString: it's purely informative and has no contract value". (as written by sir4ur0n)
你也可以参考Java语言规范文档来了解这些类型的Java API技术细节:
下面是关于这个主题的Java 11规范:https://docs.oracle.com/javase/specs/jls/se11/html/jls-6.html#jls-6.7 例6.7 - 2。例6.7-2。分别讨论了完全限定名称和完全限定名称v.规范名称
除了Nick Holt的观察之外，我还运行了一些Array数据类型的案例:
//primitive Array
int demo[] = new int[5];
Class<? extends int[]> clzz = demo.getClass();
System.out.println(clzz.getName());
System.out.println(clzz.getCanonicalName());
System.out.println(clzz.getSimpleName());
System.out.println();
//Object Array
Integer demo[] = new Integer[5];
Class<? extends Integer[]> clzz = demo.getClass();
System.out.println(clzz.getName());
System.out.println(clzz.getCanonicalName());
System.out.println(clzz.getSimpleName());
上面的代码片段打印:
[I
int[]
int[]
[Ljava.lang.Integer;
java.lang.Integer[]
Integer[]
public void printReflectionClassNames(){
StringBuffer buffer = new StringBuffer();
Class clazz= buffer.getClass();
System.out.println("Reflection on String Buffer Class");
System.out.println("Name: "+clazz.getName());
System.out.println("Simple Name: "+clazz.getSimpleName());
System.out.println("Canonical Name: "+clazz.getCanonicalName());
System.out.println("Type Name: "+clazz.getTypeName());
}
outputs:
Reflection on String Buffer Class
Name: java.lang.StringBuffer
Simple Name: StringBuffer
Canonical Name: java.lang.StringBuffer
Type Name: java.lang.StringBuffer
这是我找到的描述getName()， getSimpleName()， getCanonicalName()的最好的文档
https://javahowtodoit.wordpress.com/2014/09/09/java-lang-class-what-is-the-difference-between-class-getname-class-getcanonicalname-and-class-getsimplename/
// Primitive type
int.class.getName(); // -> int
int.class.getCanonicalName(); // -> int
int.class.getSimpleName(); // -> int
// Standard class
Integer.class.getName(); // -> java.lang.Integer
Integer.class.getCanonicalName(); // -> java.lang.Integer
Integer.class.getSimpleName(); // -> Integer
// Inner class
Map.Entry.class.getName(); // -> java.util.Map$Entry
Map.Entry.class.getCanonicalName(); // -> java.util.Map.Entry
Map.Entry.class.getSimpleName(); // -> Entry
// Anonymous inner class
Class<?> anonymousInnerClass = new Cloneable() {}.getClass();
anonymousInnerClass.getName(); // -> somepackage.SomeClass$1
anonymousInnerClass.getCanonicalName(); // -> null
anonymousInnerClass.getSimpleName(); // -> // An empty string
// Array of primitives
Class<?> primitiveArrayClass = new int[0].getClass();
primitiveArrayClass.getName(); // -> [I
primitiveArrayClass.getCanonicalName(); // -> int[]
primitiveArrayClass.getSimpleName(); // -> int[]
// Array of objects
Class<?> objectArrayClass = new Integer[0].getClass();
objectArrayClass.getName(); // -> [Ljava.lang.Integer;
objectArrayClass.getCanonicalName(); // -> java.lang.Integer[]
objectArrayClass.getSimpleName(); // -> Integer[]
有趣的是，当类名格式错误时，getCanonicalName()和getSimpleName()会引发InternalError。这种情况发生在一些非java JVM语言上，例如Scala。
考虑以下(Java 8上的Scala 2.11):
scala> case class C()
defined class C
scala> val c = C()
c: C = C()
scala> c.getClass.getSimpleName
java.lang.InternalError: Malformed class name
at java.lang.Class.getSimpleName(Class.java:1330)
... 32 elided
scala> c.getClass.getCanonicalName
java.lang.InternalError: Malformed class name
at java.lang.Class.getSimpleName(Class.java:1330)
at java.lang.Class.getCanonicalName(Class.java:1399)
... 32 elided
scala> c.getClass.getName
res2: String = C
对于混合语言环境或动态加载字节码的环境，例如应用程序服务器和其他平台软件，这可能是一个问题。
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