java 又一摘要 Reflection

Only inner classes can be private.
Regular classes always have either package or public visibility.

inner class:If an inner class has constructors, the compiler modifies them,
adding a parameter for the outer class reference.
An inner class method gets to access both its own data fields
and those of the outer object creating it.

inner class -> local inner class -> anonymous inner class

Whenever you would use a function pointer in C++,
you should consider using an interface in Java.
we suggest that you use Method objects in your own programs
only when absolutely necessary. Using interfaces and inner
classes is almost always a better idea. In particular, we echo
the developers of Java and suggest not using Method objects
for callback functions. Using interfaces for the callbacks
leads to code that runs faster and is a lot more maintainable.
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Using Reflection to Analyze the Capabilities of Classes
Example 5-5. ReflectionTest.java
1. import java.util.*;
2. import java.lang.reflect.*;
3.
4. public class ReflectionTest
5. {
6. public static void main(String[] args)
7. {
8. // read class name from command-line args or user input
9. String name;
10. if (args.length > 0)
11. name = args[0];
12. else
13. {
14. Scanner in = new Scanner(System.in);
15. System.out.println("Enter class name (e.g. java.util.Date): ");
16. name = in.next();
17. }
18.
19. try
20. {
21. // print class name and superclass name (if != Object)
22. Class cl = Class.forName(name);
23. Class supercl = cl.getSuperclass();
24. System.out.print("class " + name);
25. if (supercl != null && supercl != Object.class)
26. System.out.print(" extends " + supercl.getName());
27.
28. System.out.print("{");
29. printConstructors(cl);
30. System.out.println();
31. printMethods(cl);
32. System.out.println();
33. printFields(cl);
34. System.out.println("}");
35. }
36. catch(ClassNotFoundException e) { e.printStackTrace(); }
37. System.exit(0);
38. }
39.
40.
44. public static void printConstructors(Class cl)
45. {
46. Constructor[] constructors = cl.getDeclaredConstructors();
47.
48. for (Constructor c : constructors)
49. {
50. String name = c.getName();
51. System.out.print(" " + Modifier.toString(c.getModifiers()));
52. System.out.print(" " + name + "(");
53.
54. // print parameter types
55. Class[] paramTypes = c.getParameterTypes();
56. for (int j = 0; j < paramTypes.length; j++)
57. {
58. if (j > 0) System.out.print(", ");
59. System.out.print(paramTypes[j].getName());
60. }
61. System.out.println(");");
62. }
63. }
64.
65.
69. public static void printMethods(Class cl)
70. {
71. Method[] methods = cl.getDeclaredMethods();
72.
73. for (Method m : methods)
74. {
75. Class retType = m.getReturnType();
76. String name = m.getName();
77.
78. // print modifiers, return type and method name
79. System.out.print(" " + Modifier.toString(m.getModifiers()));
80. System.out.print(" " + retType.getName() + " " + name + "(");
81.
82. // print parameter types
83. Class[] paramTypes = m.getParameterTypes();
84. for (int j = 0; j < paramTypes.length; j++)
85. {
86. if (j > 0) System.out.print(", ");
87. System.out.print(paramTypes[j].getName());
88. }
89. System.out.println(");");
90. }
91. }
92.
93.
97. public static void printFields(Class cl)
98. {
99. Field[] fields = cl.getDeclaredFields();
100.
101. for (Field f : fields)
102. {
103. Class type = f.getType();
104. String name = f.getName();
105. System.out.print(" " + Modifier.toString(f.getModifiers()));
106. System.out.println(" " + type.getName() + " " + name + ";");
107. }
108. }
109. }
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Using Reflection to Analyze Objects at Run Time
Example 5-6. ObjectAnalyzerTest.java
1. import java.lang.reflect.*;
2. import java.util.*;
3. import java.text.*;
4.
5. public class ObjectAnalyzerTest
6. {
7. public static void main(String[] args)
8. {
9. ArrayList squares = new ArrayList();
10. for (int i = 1; i <= 5; i++) squares.add(i * i);
11. System.out.println(new ObjectAnalyzer().toString(squares));
12. }
13. }
14.
15. class ObjectAnalyzer
16. {
17.
24. public String toString(Object obj)
25. {
26. if (obj == null) return "null";
27. if (visited.contains(obj)) return "...";
28. visited.add(obj);
29. Class cl = obj.getClass();
30. if (cl == String.class) return (String) obj;
31. if (cl.isArray())
32. {
33. String r = cl.getComponentType() + "[]{";
34. for (int i = 0; i < Array.getLength(obj); i++)
35. {
36. if (i > 0) r += ",";
37. Object val = Array.get(obj, i);
38. if (cl.getComponentType().isPrimitive()) r += val;
39. else r += toString(val);
40. }
41. return r + "}";
42. }
43.
44. String r = cl.getName();
45. // inspect the fields of this class and all superclasses
46. do
47. {
48. r += "[";
49. Field[] fields = cl.getDeclaredFields();
50. AccessibleObject.setAccessible(fields, true);
51. // get the names and values of all fields
52. for (Field f : fields)
53. {
54. if (!Modifier.isStatic(f.getModifiers()))
55. {
56. if (!r.endsWith("[")) r += ",";
57. r += f.getName() + "=";
58. try
59. {
60. Class t = f.getType();
61. Object val = f.get(obj);
62. if (t.isPrimitive()) r += val;
63. else r += toString(val);
64. }
65. catch (Exception e) { e.printStackTrace(); }
66. }
67. }
68. r += "]";
69. cl = cl.getSuperclass();
70. }
71. while (cl != null);
72.
73. return r;
74. }
75.
76. private ArrayList