java高薪之路__001_类

 1 protected Class<!--?--> loadClass(String name, boolean resolve)throws ClassNotFoundException{
 2          //加上锁，同步处理，因为可能是多线程在加载类
 3          synchronized (getClassLoadingLock(name)) {
 4              //检查，是否该类已经加载过了，如果加载过了，就不加载了
 5              Class c = findLoadedClass(name);
 6              if (c == null) {
 7                  long t0 = System.nanoTime();
 8                  try {
 9                      //如果自定义的类加载器的parent不为null,就调用parent的loadClass进行加载类
10                      if (parent != null) {
11                          c = parent.loadClass(name, false);
12                      } else {
13                          //如果自定义的类加载器的parent为null，就调用findBootstrapClass方法查找类，就是Bootstrap类加载器
14                          c = findBootstrapClassOrNull(name);
15                      }
16                  } catch (ClassNotFoundException e) {
17                      // ClassNotFoundException thrown if class not found
18                      // from the non-null parent class loader
19                  }
20  
21                  if (c == null) {
22                      // If still not found, then invoke findClass in order
23                      // to find the class.
24                      long t1 = System.nanoTime();
25                      //如果parent加载类失败，就调用自己的findClass方法进行类加载
26                      c = findClass(name);
27  
28                      // this is the defining class loader; record the stats
29                      sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
30                      sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
31                      sun.misc.PerfCounter.getFindClasses().increment();
32                  }
33              }
34              if (resolve) {
35                  resolveClass(c);
36              }
37              return c;
38          }
39      }