public static void main(String[] args) {
List<Frob> list = new ArrayList<Frob>();
Map<Frob, Fnorkle> map = new HashMap<Frob, Fnorkle>();
Quark<Fnorkle> quark = new Quark<Fnorkle>();
Particle<Long, Double> p = new Particle<Long, Double>();
System.out.println(Arrays.toString(list.getClass().getTypeParameters()));
System.out.println(Arrays.toString(map.getClass().getTypeParameters()));
System.out.println(Arrays.toString(quark.getClass().getTypeParameters()));
System.out.println(Arrays.toString(p.getClass().getTypeParameters()));
}
public void testExactStringStringMap() throws Exception {
ObjectMapper mapper = new ObjectMapper();
// to get typing, must use type reference
String JSON = "{ \"a\" : \"b\" }";
Map<String, Integer> result =
mapper.readValue(JSON, new TypeReference<TreeMap<String, String>>() {});
assertNotNull(result);
assertEquals(TreeMap.class, result.getClass());
assertEquals(1, result.size());
assertEquals("b", result.get("a"));
assertNull(result.get("b"));
}
public static void performTest(final Map<String, Integer> m) throws Exception {
out.println("Test started for: " + m.getClass());
long avgTime = 0;
for (int i = 0; i < 5; i++) {
long startTime = System.nanoTime();
ExecutorService exService = Executors.newFixedThreadPool(POOL_SIZE);
for (int j = 0; j < POOL_SIZE; j++) {
exService.execute(
new Runnable() {
@SuppressWarnings("unused")
public void run() {
for (int i = 0; i < 500000; i++) {
Integer randomNum = (int) Math.ceil(Math.random() * 550000);
// Retrieve value. We are not using it anywhere
Integer value = m.get(String.valueOf(randomNum));
// Put value
m.put(String.valueOf(randomNum), randomNum);
}
}
});
}
// Make sure executor stops
exService.shutdown();
// Blocks until all tasks have completed execution after a shutdown request
exService.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS);
long entTime = System.nanoTime();
long totalTime = (entTime - startTime) / 1000000L;
avgTime += totalTime;
out.println("500K entried added/retrieved in " + totalTime + " ms");
}
out.println("For " + m.getClass() + " the average time is " + avgTime / 5 + " ms\n");
}
/**
* Let's also check that it is possible to do type conversions to allow use of non-String Map
* keys.
*/
public void testIntBooleanMap() throws Exception {
ObjectMapper mapper = new ObjectMapper();
// to get typing, must use type reference
String JSON = "{ \"1\" : true, \"-1\" : false }";
Map<String, Integer> result =
mapper.readValue(JSON, new TypeReference<HashMap<Integer, Boolean>>() {});
assertNotNull(result);
assertEquals(HashMap.class, result.getClass());
assertEquals(2, result.size());
assertEquals(Boolean.TRUE, result.get(Integer.valueOf(1)));
assertEquals(Boolean.FALSE, result.get(Integer.valueOf(-1)));
assertNull(result.get("foobar"));
assertNull(result.get(0));
}
public void testExactStringIntMap() throws Exception {
ObjectMapper mapper = new ObjectMapper();
// to get typing, must use type reference
String JSON = "{ \"foo\" : 13, \"bar\" : -39, \n \"\" : 0 }";
Map<String, Integer> result =
mapper.readValue(JSON, new TypeReference<HashMap<String, Integer>>() {});
assertNotNull(result);
assertEquals(HashMap.class, result.getClass());
assertEquals(3, result.size());
assertEquals(Integer.valueOf(13), result.get("foo"));
assertEquals(Integer.valueOf(-39), result.get("bar"));
assertEquals(Integer.valueOf(0), result.get(""));
assertNull(result.get("foobar"));
assertNull(result.get(" "));
}
/**
* ArrayList<String>和ArrayList<Integer>很容易认为是不同的类型， 不同的类型在行为方面肯定不同 但输出发现c1==c2为true
*
* @param args
*/
public static void main(String[] args) {
Class c1 = new ArrayList<String>().getClass();
Class c2 = new ArrayList<Integer>().getClass();
System.out.println(c1 == c2); // 输出为true
List<Frob> list = new ArrayList<Frob>();
Map<Frob, Fnorkle> map = new HashMap<Frob, Fnorkle>();
Quark<Fnorkle> quark = new Quark<Fnorkle>();
Particle<Long, Double> part = new Particle<Long, Double>();
// Class.getTypeParameters()将返回一个Typeariable对象数组，表示有泛型声明
// 的类型参数...
System.out.println(Arrays.toString(list.getClass().getTypeParameters()));
System.out.println(Arrays.toString(map.getClass().getTypeParameters()));
System.out.println(Arrays.toString(quark.getClass().getTypeParameters()));
System.out.println(Arrays.toString(part.getClass().getTypeParameters()));
/** 输出结果： [E] [K, V] [Q] [POSITION, MOMENTUM] */
/**
* 输出结果是一些占位符 说明：在泛型代码内部，无法获得任何有关泛型参数类型的信息。 当你在使用泛型时，任何具体的类型信息都被擦除了，你唯一知道的就是你在使用一个对象。
* 因此，List<String>和List<Integer>在运行时事实上是相同的类型。这两种形式都被 擦除成它们的原生类型，即List
*/
}
protected String buildSnippetAssertMap(String expression, Map value) {
Random r = new Random();
String type = value.getClass().getCanonicalName();
String localVar = "map_" + Math.abs(r.nextInt());
String newCollection = type + " " + localVar + " = new " + type + "<Object, Object>();";
Set<Map.Entry> set = value.entrySet();
for (Map.Entry v : set) {
newCollection +=
"\n\t"
+ localVar
+ ".put("
+ printPrimitiveString(v.getKey())
+ ", "
+ printPrimitiveString(v.getValue())
+ ");\n";
}
newCollection +=
"\t" + junitAssertClassName + ".assertEquals(" + localVar + ", " + expression + ");";
return newCollection;
}