protected synchronized Class<?> loadClass(Stirng name,boolean resolve) throws ClassNotFoundException {
	Class c = findLoadedClass(name);
	if(c == null){
		try{
			if(parent != null){
				//父类加载器存在，继续调用父类加载器的loadClass方法
				c = parent.loadClass(name,false);
			}else{
				//父类加载器不存在，调用启动类加载器去加载
				c = findBootstrapClassOrNull(name);
			}
		} catch (ClassNotFoundException e){
			
		}
		//如果父类加载器和启动类加载器都加载失败，使用当前类加载器去加载
		if ( c == null ){
			c = findClass(name);
		}
	}
	if(resolve){
		resolveClass(c);
	}
	return c;
}

//libcore/dalvik/src/main/java/dalvik/system/BaseDexClassLoader.java
Class BaseDexClassLoader extends ClassLoader{

	private final DexPathList pathList;
	//一个ClassLoader数组，用来加载pathList pathList中可能依赖的类和资源，用来实现	
	//Android中的AndroidManifest.xml中<use-library>标签中的库
	protected final ClassLoader[] sharedLibraryLoaders;
	protected final ClassLoader[] sharedLibraryLoadersAfter;
	
	public BaseDexClassLoader(String dexPath,String librarySearchPath,
		ClassLoader parent,ClassLoader[] sharedLibraryLoaders,
		ClassLoader[] sharedLibraryLoadersAfter,boolean isTrust){
		super(parent);
		...
		this.pathList = new DexPathList(this,dexPath,librarySearchPath,null,isTrust);
		
	
	}
	
	
	protected synchronized Class<?> findClass(Stirng name,boolean resolve) throws ClassNotFoundException {
	
		if(sharedLibraryLoaders != null){
			for(ClassLoader loader : sharedLibraryLoaders){
				try{
					return loader.loadClass(name);
				}catch(ClassNotFoundException ignore){
				}
			}
		}
		List<Throwable> suppressedExceptions = new ArrayList<Throwable>();
		Class c = dexPath.findClass(name,suppressedExceptions);
		if(c == null){
			return c;
		}
		if(sharedLibraryLoadersAfter != null){
			for(ClassLoader loader : sharedLibraryLoadersAfter){
				try{
					return loader.loadClass(name);
				}catch(ClassNotFoundException ignore){
				}
			}
		}
		if(c == null){
			throw new ClassNotFoundException();
		}
		return c;
	}
}

//libcore/dalvik/src/main/java/dalvik/system/DexPathList.java
class DexPathList{
	Element[] dexElements;
	public DexPathList(...){
		...
		dexElement = makePathElements(spliteDexPath(dexPath)
			,null,null,classLoader,	isTrust);
		
		...
	}
	
	
	//这里有关于热修复实现的知识点，就是将补丁 dex 文件放到 dexElements 数组靠前位置，
	//这样在加载 class 时，优先找到补丁包中的 dex 文件，加载到 class 之后就不再寻找，从
	//而原来的 apk 文件中同名的类就不会再使用，从而达到修复的目的

	public Class<?> findClass(String name,List<Throwable> suppressed){
		for(Element element : dexElements){
			Class<?> clazz = element.findClass(name,classLoader,suppressed);
			if(clazz != null){
				return clazz;
			}
		}
		return null;
	}
	
	public static Element[] makeDexElements(List<File> files,File optimizedDictionary,List<IOException> suppressedExceptions,ClassLoader classloader,boolean isTrusted){
		Element[] elements = new Element[files.size()];
		
		for(Files file : files){
			if(file.isDictionary()){
				elements[elementsPos++] = new Element(file);
			}else{
				if(file.isFile()){
					DexFile dex = null;
					if(file.path.endWith(".dex")){
						dex = loadDexFile(file,optimizedDictionary,loader,elements);
						if(dex != null){
							elements[elementsPos++] = new Element(dex,null);
						}
					}else{
						dex = loadDexFile(file,optimizedDictionary,loader,elements);
						if(dex == null){
							elements[elementsPos++] = new Element(file);
						}else{
							elements[elementsPos++] = new Element(dex,file);
						}
					}
				}
			}
		}
		return elements;
	}
	
	
	private static DexFile loadDexPath(File file,File optimizedDictionary,ClassLoader loader,Element[] elements){
		if(optimizeDictory == null){
			return new DexFile(file,loader,elements);
		}else{
			//创建一个文件，路径为optimizedDictionary指定文件夹内，file同名的文件。
			String optimizedPath = optimizedPathFor(file,optimizedDictionary);
			...
		}
	}
}




//libcore/dalvik/src/main/java/dalvik/system/DexFile.java

final Class DexFile{
	private Object mCookie;
	
	public DexFile(File file,ClassLoader loader,DexPathList.Element[] elements){
		mCookie = openDexFile(...);
	}
	
	
	private static Object openDexFile(){
		return openDexFileNative(...);
	}
}