比较java中的字符串

String str = "Hello, world!";

String str = new String("Hello, world!");

String str = "Hello, world!";
int len = str.length();

String str1 = "Hello, ";
String str2 = "world!";
String str3 = str1 + str2;

String str1 = "Hello, ";
String str2 = "world!";
StringBuilder sb = new StringBuilder();
sb.append(str1).append(str2);
String str3 = sb.toString();

String str1 = "Hello, world!";
String str2 = "Hello, world!";
if (str1.equals(str2)) {
    System.out.println("The two strings are equal.");
}

String str1 = "Hello, world!";
String str2 = "Hello, world!";
if (str1 == str2) {
    System.out.println("The two strings are equal.");
}

String str = "Hello, world!";
String[] arr = str.split(", ");