java learning - Compare string methods

/ *
== is a comparison target address value, the contents if you really need string comparison, two methods may be used:

public boolean equals (Object obj): parameter can be any object, only parameter is a string and the same content will give true; otherwise false.
Precautions:

1. Any object can receive with Object.
2. equals method has symmetry, i.e. a.equals (b) and b.equals (a) the same effect.
3. If the two sides compare a constant to a variable, the constant string EDITORIAL recommended.
   Recommended: "abc" .equals (str) is not recommended: str.equals ( "abc")

public boolean equalsIgnoreCase (String str): Ignore case, the content comparison.
* /

public class Demo01StringEquals {

    public static void main(String[] args) {
        String str1 = "Hello";
        String str2 = "Hello";
        char[] charArray = {'H', 'e', 'l', 'l', 'o'};
        String str3 = new String(charArray);

        System.out.println(str1.equals(str2)); // true
        System.out.println(str2.equals(str3)); // true
        System.out.println(str3.equals("Hello")); // true
        System.out.println("Hello".equals(str1)); // true

        String str4 = "hello";
        System.out.println(str1.equals(str4)); // false
        System.out.println("=================");

        String str5 = null;
        System.out.println("abc".equals(str5)); // 推荐：false
//        System.out.println(str5.equals("abc")); // 不推荐：报错，空指针异常NullPointerException
        System.out.println("=================");

        String strA = "Java";
        String strB = "java";
        System.out.println(strA.equals(strB)); // false，严格区分大小写
        System.out.println(strA.equalsIgnoreCase(strB)); // true，忽略大小写

        // 注意，只有英文字母区分大小写，其他都不区分大小写
        System.out.println("abc一123".equalsIgnoreCase("abc壹123")); // false
    }

}