一,基本数据类型

八种基本类型有默认值

 

二,String 对象

// 判断String为空//String s = "";//String s = null;String s = " ";s = s.trim(); // 处理" "// 方法1if (s == null || "".equals(s)) { // null,""," "    System.out.println("String 为空1");}// 方法2if (s == null || s.length() <= 0) { // 推荐  // null,""," "    System.out.println("String 为空2");} else if (s.length() == 1 && Character.isWhitespace(s.charAt(0)) == true) {    System.out.println("String 为空5");}// 方法3if (s == null || s.isEmpty()) { // null,""," "    System.out.println("String 为空3");}// 方法4if (s == null || s == "") { // 不推荐 // null,""    System.out.println("String 为空4");}

apache工具类

StringUtils.isBlank(s) 

 

三,数组

// 判断数组为空//String[] arr = null;String[] arr = new String[0];//String[] arr = new String[2]; // 有长度,不为空if (arr == null || arr.length == 0) {    System.out.println("数组 为空1");}

 apache工具类

ArrayUtils.isEmpty(arr) 

 

四,集合(List,Map,Set)

// 判断list为空（Map、Set同list）//List
     
       strList = null;List
      
        strList = new ArrayList
       
        ();if (strList == null || strList.size() == 0) {    System.out.println("list 为空1");}if (strList == null || strList.isEmpty()) { // 推荐    System.out.println("list 为空2");}
       
      
     

 spring工具类

CollectionUtils.isEmpty(strList);