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

男娘i 2022-09-11 05:18 36阅读 0赞

### 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