31字符串— String:示例 public class String Demo2 i public static void main(String args[l) t String strobl="First String String strob2=Second String", String strob3= strObl System. out. println("Length of strObl: +strObl. length) System. out. println("Char at index 3 in strobl: +strObl. charAt(3)) if(strobl. equals(strob2)) System. out println (strObl== strOb2) else System. out. println(strobl!= strOb2 ) if(strObl.equals(strOb3)) System. out. printIn(strobl==strOb3") else System. out. printIn(strobl!=strob3");public class StringDemo2 { public static void main(String args[]) { String strOb1 = "First String"; String strOb2 = "Second String"; String strOb3 = strOb1; System.out.println("Length of strOb1: " +strOb1.length()); System.out.println("Char at index 3 in strOb1: " +strOb1.charAt(3)); if(strOb1.equals(strOb2)) System.out.println("strOb1 = = strOb2"); else System.out.println("strOb1 != strOb2"); if(strOb1.equals (strOb3)) System.out.println("strOb1 == strOb3"); else System.out.println("strOb1 != strOb3"); } } 3.1字符串——String：示例