基础数据类型长度

public class C3 { 
    //default 8 
    public byte b = 2 ; //1 
    
    public short s = 2 ; //2 
    public char c = '2' ; //2 
    
    public int i = 2 ; //4 
    public float f = 2.0f ; //4 
    
    public double d = 2.0 ; //8 
    public long l = 2l ; //8 
    
    public String str = "1" ; //4 
    //total 41 
} 

//上面忘了测试boolean，测试工具为“visualvm”

public class C4 extends C3 { 
    //C3类型部分 大小 41 
    public int i = 23 ; //4 
    public Object obj ; //4 
    public Object obj2 = null ; //4 
    public Object obj3 = new Object(); //4 
    public Object obj4 = new C3(); //4 
    public C3 c3 = new C3(); //4 
    //总占用 65 
    //这里的占用内存多少，并没有计算对象类型变量实例（如new Object()、new C3()）所占内存 
    //如：在这个类的实例中生成了两个“C3”类型对象共用去82byte内存（也没计算内部对象所占内存） 
}