什么是引用数据类型以及引用和基本数据类型的默认初始值

    private int a;
    private byte b;
    private short c;
    private char d;
    private long e;
    private double f;
    private float g;
    private boolean h;
    private String string;
    
    public static void main(String[] args) {
        Inialization inialization = new Inialization();
        System.out.println("int型初始值:"+inialization.a);
        System.out.println("byte型初始值:"+inialization.b);
        System.out.println("short型初始值:"+inialization.c); 
        System.out.println("char型初始值:"+inialization.d);
        System.out.println("long型初始值:"+inialization.e);
        System.out.println("double型初始值:"+inialization.f);
        System.out.println("float型初始值:"+inialization.g);
        System.out.println("boolean型初始值:"+inialization.h);
        System.out.println("string型初始值:"+inialization.string);
        
    }