String aa = "aa";
aa.replace("a", "b");
System.out.println(aa);
aa.replace("b", "a");
System.out.println(aa);
aa.replaceAll("a", "b");
System.out.println(aa);
aa.replaceAll("b", "a");
System.out.println(aa);输出结果都是aa
String aa = "aa";
aa.replace("a", "b");
System.out.println(aa);
aa.replace("b", "a");
System.out.println(aa);
aa.replaceAll("a", "b");
System.out.println(aa);
aa.replaceAll("b", "a");
System.out.println(aa);输出结果都是aa