equalsIgnoreCase忽略大小写直接对比

String s1 = "Hello World";
String s2 = "hello world";
String s3 = "HELLO WORLD";
String s4 = "Hello Java";

System.out.println(s1.equals(s2)); // false
System.out.println(s1.equalsIgnoreCase(s2)); // true
System.out.println(s1.equalsIgnoreCase(s3)); // true
System.out.println(s1.equalsIgnoreCase(s4)); // false
空值处理与equals一置