UnSafe类初探

UnSafe类初探

package com.fjl;
import java.lang.reflect.Field;

import sun.misc.Unsafe;


class A{
	private String name;

	public A(String name) {
		this.name = name;
	}
	@Override
	public String toString() {
		return this.name;
	}
}
@SuppressWarnings("restriction")
public class TestUnsafe {
	static final Unsafe unsafe;
	static final long stateOffset;
	private volatile long state=0;
	private volatile  A a=new A("a1");
	static {
//		unsafe=getUnsafe();
//		stateOffset=get();
		try {
			Field field = Unsafe.class.getDeclaredField("theUnsafe");
			field.setAccessible(true);
			unsafe = (Unsafe)field.get(null);
//			stateOffset =unsafe.objectFieldOffset(TestUnsafe.class.getDeclaredField("state"));
			stateOffset =unsafe.objectFieldOffset(TestUnsafe.class.getDeclaredField("a"));
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
			throw new RuntimeException(e);  
//			unsafe = null;a
//			stateOffset =0l;
		}
	}
	private static Unsafe getUnsafe() {
		try {
			Field field = Unsafe.class.getDeclaredField("theUnsafe");
			field.setAccessible(true);
			return  (Unsafe)field.get(null);
			
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		
		// TODO Auto-generated method stub
		return null;
	}
	private static long get() {
		// TODO Auto-generated method stub
		try {
			return unsafe.objectFieldOffset(TestUnsafe.class.getDeclaredField("a"));
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} 
		return 0L;
	}
	
	public static void main(String[] args) {
		TestUnsafe t = new TestUnsafe();
		Long i=t.state;
//		unsafe.compareAndSwapInt(t, stateOffset, 0, 1);
		System.out.println(t.a);
		A a3=t.a;
		System.out.println(stateOffset);
		boolean compareAndSwapObject = unsafe.compareAndSwapObject(t, stateOffset, a3, new A("a2"));
		System.out.println("compareAndSwapObject="+compareAndSwapObject);
//		System.out.println(t.state);
//		System.out.println(i);
		System.out.println(t.a);
		System.out.println(a3);
	}

}


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