Java - 一篇带你了解类成员（基本数据类型/包装类/对象/数组）默认值

Posted 2021-09-30 程序员牧码

代码 

/**
 * @author Lux Sun
 * @date 2021/9/13
 */
public class DefaultValueDemo {

    private byte byteValue;

    private short shortValue;

    private int intValue;

    private long longValue;

    private float floatValue;

    private double doubleValue;

    private char charValue;

    private char[] charArrayValue;

    private boolean booleanValue;

    private boolean[] booleanArrayValue;

    private Byte byteVal;

    private Short shortVal;

    private Integer integerVal;

    private Long longVal;

    private Float floatVal;

    private Double doubleVal;

    private Character characterVal;

    private Boolean booleanVal;

    private Boolean[] booleanArrayVal;

    private String stringVal;

    private String[] stringArrayVal;

    private Object objectVal;

    public static void main(String[] args) {
        DefaultValueDemo demo = new DefaultValueDemo();
        System.out.println("byte: " + demo.byteValue); // (byte)0
        System.out.println("short: " + demo.shortValue); // (short)0
        System.out.println("int: " + demo.intValue);
        System.out.println("long: " + demo.longValue); // 0L
        System.out.println("float: " + demo.floatValue); // 0.0f
        System.out.println("double: " + demo.doubleValue); // 0.0d
        System.out.println("char: " + demo.charValue); // '\\u0000' 什么也不输出, 不要认为输出是空格
        System.out.println("char[]: " + demo.charArrayValue);
        System.out.println("boolean: " + demo.booleanValue);
        System.out.println("Byte: " + demo.byteVal);
        System.out.println("Short: " + demo.shortVal);
        System.out.println("Integer: " + demo.integerVal);
        System.out.println("Long: " + demo.longVal);
        System.out.println("Float: " + demo.floatVal);
        System.out.println("Double: " + demo.doubleVal);
        System.out.println("Character: " + demo.characterVal);
        System.out.println("Boolean: " + demo.booleanVal);
        System.out.println("String: " + demo.stringVal);
        System.out.println("String[]: " + demo.stringArrayVal);
        System.out.println("Object: " + demo.objectVal);
        System.out.println("boolean[]: " + demo.booleanArrayValue);
        System.out.println("Boolean[]: " + demo.booleanArrayVal);
    }
}

输出 

byte: 0
short: 0
int: 0
long: 0
float: 0.0
double: 0.0
char:  
char[]: null
boolean: false
Byte: null
Short: null
Integer: null
Long: null
Float: null
Double: null
Character: null
Boolean: null
String: null
String[]: null
Object: null
boolean[]: null
Boolean[]: null

总结

• 所有对象、数组、包装类默认值：null

• 只需记住基本数据类型默认值即可，特殊了解的已经在代码里标注