类String的学习1

String 类代表字符串.
下面通过实例学习：
public class ToString {
public static void main(String[] args) {
String s1 = “hello world”;
String s2 = “hello world”;

    String s3 = "hello" + " world";

    String s4 = new String("hello world");
    String s5 = new String("hello world");

    System.out.println(s1 == s2);
    System.out.println(s1.equals(s2));

    System.out.println("--------------");

    System.out.println(s1 == s3);
    System.out.println(s1.equals(s3));

    System.out.println("--------------");

    System.out.println(s1 == s4);
    System.out.println(s1.equals(s4));

    System.out.println("--------------");

    System.out.println(s4 == s5);
    System.out.println(s4.equals(s5));

    System.out.println("--------------");
    test1();

}

public static void test1() {
    String s1 = "Hello";
    String s2 = "hello";
    //s1字符串与对象s2比较
    boolean isEquals = s1.equals(s2);
    System.out.println(isEquals);
}

public static void test2() {
    String s1 = "Hello";
    String s2 = "hello";
    //不考虑大小写的比较
    boolean isEquals = s1.equalsIgnoreCase(s2);
    System.out.println(isEquals);
}

public static void test3() {
    String s1 = "Hello521";
    String s2 = "llo1521";
    //字符串包含指定的 char 值序列时，返回 true
    boolean contains = s1.contains(s2);
    System.out.println(contains);
}

public static void test4() {
    String s1 = "Hello521";
    String s2 = "Hel";
    //测试字符串是否以指定的前缀开始
    boolean startsWith = s1.startsWith(s2);
    System.out.println(startsWith);
}

public static void test5() {
    String s1 = "";
    //字符串为空时
    boolean empty = s1.isEmpty();
    System.out.println(empty);
}

}

运行结果1：
true
true

---

true
true

---

false
true

---

false
true

---

false
true
false
true
true