public static void main(String\[\] args) {
String a = new String();
String b = "";
String c = null;
if (a.isEmpty()) {
System.out.println("String a is empty");
}
if (b.isEmpty()) {
System.out.println("String b is empty");
}
if (c == null) {
System.out.println("String c = null");
}
if (null == a) {
// 编译器直接就提示了Dead code,a指向了一个新对象,肯定不是null了
System.out.println("String a =null");
}
if (a == "") {
System.out.println("a = ''");
}
if (a.equals("")) {
//由于a是字符串,字符串的比较需要用equals,不能直接用 ==
System.out.println("a = ''");
}
/*if (c.isEmpty()) {
// 这里会报空指针,即null不能使用此方法
System.out.println("c == null and c.isEmpty");
}*/
List<String> list = new ArrayList<>();
//list.add("");
if (list.isEmpty()) {
System.out.println("list is empty");
}
System.out.println(list.size());
}
/*Output:
String a is empty
String b is empty
String c = null
equals:a = ''
list is empty
0
*/