blic native void freeMemory(long address)
举个栗子：
public void test() throws Exception {
Unsafe unsafe = getUnsafe();
long address = unsafe.allocateMemory(8);
System.out.println("allocate memory with 8 bytes, address=" + address);
long data = 13579L;
unsafe.putLong(address, data);
System.out.println("direct put data to address, data=" + data);
System.out.println("get address data=" + unsafe.getLong(address));
long address1 = unsafe.allocateMemory(8);
System.out.println("allocate memory with 8 bytes, address1=" + address);
unsafe.copyMemory(address, address1, 8);
System.out.println("copy memory with 8 bytes to address1=" + address1);
System.out.println("get address1 data=" + unsafe.getLong(address1));
unsafe.reallocateMemory(address1, 16);
unsafe.setMemory(address1, 16, (byte)20);
System.out.println("after setMemory address1=" + unsafe.getByte(address1));
unsafe.freeMemory(address1);
unsafe.freeMemory(address);
System.out.println("free memory over");
long[] l1 = new long[] {11, 22, 33, 44};
long[] l2 = new long[4];
long offset = unsafe.arrayBaseOffset(long[].class);
unsafe.copyMemory(l1, offset, l2, offset, 32);
System.out.println("l2=" + Arrays.toString(l2));
}
输出结果：
allocate memory with 8 bytes, address=510790256
direct put data to address, data=13579
get address data=13579
allocate memory with 8 bytes, address1=510790256
copy memory with 8 bytes to address1=510788736
get address1 data=13579
after setMemory address1=20
free memory over
l2=[11, 22, 33, 44]
Unsafe操作类、对象及变量
下面介绍关于类、对象及变量相关的一些操作，还有一些其他的方法没有一一列出，大家可以自行研究。
//实例化对象，不调构造方法
Object allocateInstance(Class<?> cls)
//字段在内存中的地址相对于实例对象内存地址的偏移量
public long objectFieldOffset(Field f)
//字段在内存中的地址相对于class内存地址的偏移量
public long objectFieldOffset(Class<?> c, String name)
//静态字段在class对象中的偏移
public long staticFieldOffset(Field f)
//获得静态字段所对应类对象
public Object staticFieldBase(Field f)
//获取对象中指定偏移量的int值，这里还有基本类型的其他其中，比如char,boolean,long等
public native int getInt(Object o, long offset);
//将int值放入指定对象指定偏移量的位置，这里还有基本类型的其他其中，比如char,boolean,long等
public native void putInt(Object o, long offset, int x);
//获取obj对象指定offset的属性对象
public native Object getObject(Object obj, long offset);
//将newObj对象放入指定obj对象指定offset偏移量的位置
public native void putObject(Object obj, long offset, Object newObj);
实战一下吧
class Cat {
private String name;
private long speed;
public Cat(String name, long speed) {
this.name = name;
this.speed = speed;
}
public Cat() {
System.out.println("constructor...");
}
static {
System.out.println("static...");
}
@Override
public String toString() {
return "Cat{" + "name='" + name + '\'' + ", speed=" + speed + '}';
}
}
class Foo {
private int age;
private Cat cat;
private static String defaultString = "default........";
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Cat getCat() {
return cat;
}
public void setCat(Cat cat) {
this.cat = cat;
}
}
//测试方法
public void test1() throws Exception {
// 使用allocateInstance方法创建一个Cat实例，这里不会调用构造方法，但是静态块会执行，所以会输出"static..."
Cat cat = (Cat)unsafe.allocateInstance(Cat.class);
System.out.print