在上面那個圖,我們看到一個特殊的變量unsafe,它的包名是 sun.misc.Unsafe;從名字看,這個類應該是封裝一些不安全的操作,為什么不安全?對c語言理解的朋友就知道了,指針是不安全的,在java中把指針去除的重要原因,指針指錯位置,計算偏移,很危險的!會覆蓋別人的內存// // Source code recreated from a .class file by IntelliJ IDEA // (powered by Fernflower decompiler) // package sun.misc; import java.lang.reflect.Field; import java.lang.reflect.Modifier; import java.security.ProtectionDomain; import sun.reflect.CallerSensitive; import sun.reflect.Reflection; public final class Unsafe {private static final Unsafe theUnsafe;public static final int INVALID_FIELD_OFFSET = -1;public static final int ARRAY_BOOLEAN_BASE_OFFSET;public static final int ARRAY_BYTE_BASE_OFFSET;public static final int ARRAY_SHORT_BASE_OFFSET;public static final int ARRAY_CHAR_BASE_OFFSET;public static final int ARRAY_INT_BASE_OFFSET;public static final int ARRAY_LONG_BASE_OFFSET;public static final int ARRAY_FLOAT_BASE_OFFSET;public static final int ARRAY_DOUBLE_BASE_OFFSET;public static final int ARRAY_OBJECT_BASE_OFFSET;public static final int ARRAY_BOOLEAN_INDEX_SCALE;public static final int ARRAY_BYTE_INDEX_SCALE;public static final int ARRAY_SHORT_INDEX_SCALE;public static final int ARRAY_CHAR_INDEX_SCALE;public static final int ARRAY_INT_INDEX_SCALE;public static final int ARRAY_LONG_INDEX_SCALE;public static final int ARRAY_FLOAT_INDEX_SCALE;public static final int ARRAY_DOUBLE_INDEX_SCALE;public static final int ARRAY_OBJECT_INDEX_SCALE;public static final int ADDRESS_SIZE;private static native void registerNatives();private Unsafe() {}@CallerSensitivepublic static Unsafe getUnsafe() {Class var0 = Reflection.getCallerClass();if (!VM.isSystemDomainLoader(var0.getClassLoader())) {throw new SecurityException("Unsafe");} else {return theUnsafe;}}public native int getInt(Object var1, long var2);public native void putInt(Object var1, long var2, int var4);public native Object getObject(Object var1, long var2);public native void putObject(Object var1, long var2, Object var4);public native boolean getBoolean(Object var1, long var2);public native void putBoolean(Object var1, long var2, boolean var4);public native byte getByte(Object var1, long var2);public native void putByte(Object var1, long var2, byte var4);public native short getShort(Object var1, long var2);public native void putShort(Object var1, long var2, short var4);public native char getChar(Object var1, long var2);public native void putChar(Object var1, long var2, char var4);public native long getLong(Object var1, long var2);public native void putLong(Object var1, long var2, long var4);public native float getFloat(Object var1, long var2);public native void putFloat(Object var1, long var2, float var4);public native double getDouble(Object var1, long var2);public native void putDouble(Object var1, long var2, double var4);/** @deprecated */@Deprecatedpublic int getInt(Object var1, int var2) {return this.getInt(var1, (long)var2);}/** @deprecated */@Deprecatedpublic void putInt(Object var1, int var2, int var3) {this.putInt(var1, (long)var2, var3);}/** @deprecated */@Deprecatedpublic Object getObject(Object var1, int var2) {return this.getObject(var1, (long)var2);}/** @deprecated */@Deprecatedpublic void putObject(Object var1, int var2, Object var3) {this.putObject(var1, (long)var2, var3);}/** @deprecated */@Deprecatedpublic boolean getBoolean(Object var1, int var2) {return this.getBoolean(var1, (long)var2);}/** @deprecated */@Deprecatedpublic void putBoolean(Object var1, int var2, boolean var3) {this.putBoolean(var1, (long)var2, var3);}/** @deprecated */@Deprecatedpublic byte getByte(Object var1, int var2) {return this.getByte(var1, (long)var2);}/** @deprecated */@Deprecatedpublic void putByte(Object var1, int var2, byte var3) {this.putByte(var1, (long)var2, var3);}/** @deprecated */@Deprecatedpublic short getShort(Object var1, int var2) {return this.getShort(var1, (long)var2);}/** @deprecated */@Deprecatedpublic void putShort(Object var1, int var2, short var3) {this.putShort(var1, (long)var2, var3);}/** @deprecated */@Deprecatedpublic char getChar(Object var1, int var2) {return this.getChar(var1, (long)var2);}/** @deprecated */@Deprecatedpublic void putChar(Object var1, int var2, char var3) {this.putChar(var1, (long)var2, var3);}/** @deprecated */@Deprecatedpublic long getLong(Object var1, int var2) {return this.getLong(var1, (long)var2);}/** @deprecated */@Deprecatedpublic void putLong(Object var1, int var2, long var3) {this.putLong(var1, (long)var2, var3);}/** @deprecated */@Deprecatedpublic float getFloat(Object var1, int var2) {return this.getFloat(var1, (long)var2);}/** @deprecated */@Deprecatedpublic void putFloat(Object var1, int var2, float var3) {this.putFloat(var1, (long)var2, var3);}/** @deprecated */@Deprecatedpublic double getDouble(Object var1, int var2) {return this.getDouble(var1, (long)var2);}/** @deprecated */@Deprecatedpublic void putDouble(Object var1, int var2, double var3) {this.putDouble(var1, (long)var2, var3);}public native byte getByte(long var1);public native void putByte(long var1, byte var3);public native short getShort(long var1);public native void putShort(long var1, short var3);public native char getChar(long var1);public native void putChar(long var1, char var3);public native int getInt(long var1);public native void putInt(long var1, int var3);public native long getLong(long var1);public native void putLong(long var1, long var3);public native float getFloat(long var1);public native void putFloat(long var1, float var3);public native double getDouble(long var1);public native void putDouble(long var1, double var3);public native long getAddress(long var1);public native void putAddress(long var1, long var3);public native long allocateMemory(long var1);public native long reallocateMemory(long var1, long var3);public native void setMemory(Object var1, long var2, long var4, byte var6);public void setMemory(long var1, long var3, byte var5) {this.setMemory((Object)null, var1, var3, var5);}public native void copyMemory(Object var1, long var2, Object var4, long var5, long var7);public void copyMemory(long var1, long var3, long var5) {this.copyMemory((Object)null, var1, (Object)null, var3, var5);}public native void freeMemory(long var1);/** @deprecated */@Deprecatedpublic int fieldOffset(Field var1) {return Modifier.isStatic(var1.getModifiers()) ? (int)this.staticFieldOffset(var1) : (int)this.objectFieldOffset(var1);}/** @deprecated */@Deprecatedpublic Object staticFieldBase(Class<?> var1) {Field[] var2 = var1.getDeclaredFields();for(int var3 = 0; var3 < var2.length; ++var3) {if (Modifier.isStatic(var2[var3].getModifiers())) {return this.staticFieldBase(var2[var3]);}}return null;}public native long staticFieldOffset(Field var1);public native long objectFieldOffset(Field var1);public native Object staticFieldBase(Field var1);public native boolean shouldBeInitialized(Class<?> var1);public native void ensureClassInitialized(Class<?> var1);public native int arrayBaseOffset(Class<?> var1);public native int arrayIndexScale(Class<?> var1);public native int addressSize();public native int pageSize();public native Class<?> defineClass(String var1, byte[] var2, int var3, int var4, ClassLoader var5, ProtectionDomain var6);public native Class<?> defineAnonymousClass(Class<?> var1, byte[] var2, Object[] var3);public native Object allocateInstance(Class<?> var1) throws InstantiationException;/** @deprecated */@Deprecatedpublic native void monitorEnter(Object var1);/** @deprecated */@Deprecatedpublic native void monitorExit(Object var1);/** @deprecated */@Deprecatedpublic native boolean tryMonitorEnter(Object var1);public native void throwException(Throwable var1);public final native boolean compareAndSwapObject(Object var1, long var2, Object var4, Object var5);public final native boolean compareAndSwapInt(Object var1, long var2, int var4, int var5);public final native boolean compareAndSwapLong(Object var1, long var2, long var4, long var6);public native Object getObjectVolatile(Object var1, long var2);public native void putObjectVolatile(Object var1, long var2, Object var4);public native int getIntVolatile(Object var1, long var2);public native void putIntVolatile(Object var1, long var2, int var4);public native boolean getBooleanVolatile(Object var1, long var2);public native void putBooleanVolatile(Object var1, long var2, boolean var4);public native byte getByteVolatile(Object var1, long var2);public native void putByteVolatile(Object var1, long var2, byte var4);public native short getShortVolatile(Object var1, long var2);public native void putShortVolatile(Object var1, long var2, short var4);public native char getCharVolatile(Object var1, long var2);public native void putCharVolatile(Object var1, long var2, char var4);public native long getLongVolatile(Object var1, long var2);public native void putLongVolatile(Object var1, long var2, long var4);public native float getFloatVolatile(Object var1, long var2);public native void putFloatVolatile(Object var1, long var2, float var4);public native double getDoubleVolatile(Object var1, long var2);public native void putDoubleVolatile(Object var1, long var2, double var4);public native void putOrderedObject(Object var1, long var2, Object var4);public native void putOrderedInt(Object var1, long var2, int var4);public native void putOrderedLong(Object var1, long var2, long var4);public native void unpark(Object var1);public native void park(boolean var1, long var2);public native int getLoadAverage(double[] var1, int var2);public final int getAndAddInt(Object var1, long var2, int var4) {int var5;do {var5 = this.getIntVolatile(var1, var2);} while(!this.compareAndSwapInt(var1, var2, var5, var5 + var4));return var5;}public final long getAndAddLong(Object var1, long var2, long var4) {long var6;do {var6 = this.getLongVolatile(var1, var2);} while(!this.compareAndSwapLong(var1, var2, var6, var6 + var4));return var6;}public final int getAndSetInt(Object var1, long var2, int var4) {int var5;do {var5 = this.getIntVolatile(var1, var2);} while(!this.compareAndSwapInt(var1, var2, var5, var4));return var5;}public final long getAndSetLong(Object var1, long var2, long var4) {long var6;do {var6 = this.getLongVolatile(var1, var2);} while(!this.compareAndSwapLong(var1, var2, var6, var4));return var6;}public final Object getAndSetObject(Object var1, long var2, Object var4) {Object var5;do {var5 = this.getObjectVolatile(var1, var2);} while(!this.compareAndSwapObject(var1, var2, var5, var4));return var5;}public native void loadFence();public native void storeFence();public native void fullFence();private static void throwIllegalAccessError() {throw new IllegalAccessError();}static {registerNatives();Reflection.registerMethodsToFilter(Unsafe.class, new String[]{"getUnsafe"});theUnsafe = new Unsafe();ARRAY_BOOLEAN_BASE_OFFSET = theUnsafe.arrayBaseOffset(boolean[].class);ARRAY_BYTE_BASE_OFFSET = theUnsafe.arrayBaseOffset(byte[].class);ARRAY_SHORT_BASE_OFFSET = theUnsafe.arrayBaseOffset(short[].class);ARRAY_CHAR_BASE_OFFSET = theUnsafe.arrayBaseOffset(char[].class);ARRAY_INT_BASE_OFFSET = theUnsafe.arrayBaseOffset(int[].class);ARRAY_LONG_BASE_OFFSET = theUnsafe.arrayBaseOffset(long[].class);ARRAY_FLOAT_BASE_OFFSET = theUnsafe.arrayBaseOffset(float[].class);ARRAY_DOUBLE_BASE_OFFSET = theUnsafe.arrayBaseOffset(double[].class);ARRAY_OBJECT_BASE_OFFSET = theUnsafe.arrayBaseOffset(Object[].class);ARRAY_BOOLEAN_INDEX_SCALE = theUnsafe.arrayIndexScale(boolean[].class);ARRAY_BYTE_INDEX_SCALE = theUnsafe.arrayIndexScale(byte[].class);ARRAY_SHORT_INDEX_SCALE = theUnsafe.arrayIndexScale(short[].class);ARRAY_CHAR_INDEX_SCALE = theUnsafe.arrayIndexScale(char[].class);ARRAY_INT_INDEX_SCALE = theUnsafe.arrayIndexScale(int[].class);ARRAY_LONG_INDEX_SCALE = theUnsafe.arrayIndexScale(long[].class);ARRAY_FLOAT_INDEX_SCALE = theUnsafe.arrayIndexScale(float[].class);ARRAY_DOUBLE_INDEX_SCALE = theUnsafe.arrayIndexScale(double[].class);ARRAY_OBJECT_INDEX_SCALE = theUnsafe.arrayIndexScale(Object[].class);ADDRESS_SIZE = theUnsafe.addressSize();} }

上面那個是Unsafe類,看出很多方法都是本地方法

這簡單介紹幾個的意思,而且在給大家看下這個

根據java類的加載器原理,應用程序的類由App Loader 加載,而且系統核心類,如rt.jar中的類由Bootstrap類加載器加載,Bootstrap類加載器沒有java對象的對象,因此試圖獲得這個類加載會返回null,所以,當一個類的類加載器為null時,說明它是由Bootstrap類加載器加載的,而且這個類也極可能是rt.jar中的類

歡迎轉載,轉載請注明出處!

github: rs1314

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