java验证控制的方法

TestNullOrEmpty.java

public class TestNullOrEmpty {

    public static void main(String[] args) {
         String value = null;
         testNullOrEmpty(value);
        
         value = "";
         testNullOrEmpty(value);
        
         value = " ";
         testNullOrEmpty(value);
        
         value = "hello me! ";
         testNullOrEmpty(value);
     }
    
    static void testNullOrEmpty(String value) {
        if (value == null ) { //正确的写法
             System.out.println("value is null. ");
         } else if ("".equals(value)) { //正确的写法
             System.out.println("value is blank but not null. ");
         } else {
             System.out.println("value is /" " + value + "/" ");
         }
        
        if (value == "") {  //NG 错误的写法
        //别用这种写法
         }
     }
}

编译执行：
c:/>javac TestNullOrEmpty.java

c:/>java TestNullOrEmpty
value is null.
value is blank but not null.
value is " "
value is "hello me!"