成员变量只声明未初始化在类初始化时会赋予默认值可以直接使用；局部变量必须赋值才可以使用，如果局部变量未赋值，编译无法通过。
成员变量 @Data@ToStringpublic class Result { private byte byteTest; private short shortTest; private int intTest; private long longTest; private float floatTest; private double doubleTest; private char charTest; private boolean booleanTest; private String stringTest; private Byte testByte; private Short testShort; private Integer testInteger; private Long testLong; private Float testFloat; private Double testDouble; private Character testCharacter; private Boolean testBoolean; public static void main(String[] args) { Result result = new Result(); System.out.println("-----------基本类型----------"); System.out.println("byteTest=" + result.byteTest); System.out.println("shortTest=" + result.shortTest); System.out.println("intTest=" + result.intTest); System.out.println("longTest=" + result.longTest); System.out.println("floatTest=" + result.floatTest); System.out.println("doubleTest=" + result.doubleTest); System.out.println("charTest=" + result.charTest); System.out.println("booleanTest=" + result.booleanTest); System.out.println("-----------引用类型----------"); System.out.println("testByte=" + result.testByte); System.out.println("testShort=" + result.testShort); System.out.println("testInteger=" + result.testInteger); System.out.println("testLong=" + result.testLong); System.out.println("testFloat=" + result.testFloat); System.out.println("testDouble=" + result.testDouble); System.out.println("testCharacter=" + result.testCharacter); System.out.println("testByte=" + result.testByte); System.out.println("stringTest=" + result.stringTest); }}控制台数据结果：-----------基本类型----------byteTest=0shortTest=0intTest=0longTest=0floatTest=0.0doubleTest=0.0charTest= booleanTest=false-----------引用类型----------testByte=nulltestShort=nulltestInteger=nulltestLong=nulltestFloat=nulltestDouble=nulltestCharacter=nulltestByte=nullstringTest=null 局部变量 public static void main(String[] args) { int a; String s; System.out.println("a:" + a); }