<aside> 💁🏻 필자는 substring() 을 subtraction(뺄셈) + string(문자열)의 합성어로 생각해 접근하겠다.

</aside>

1️⃣ public String substring(int beginIndex)

public class SubStringDemo {
	
	public static void main(String[] args) {

		String a = "abc".substring(0);
		String b = "abc".substring(1);
		String c = "abc".substring(2);
		String d = "abc".substring(3);
		System.out.println(a);  //abc
		System.out.println(b);  //bc
		System.out.println(c);  //c
		System.out.println(d);  //an empty string
		//is equivalent to:
		String abc = "abc";
		String d = abc.substring(0);
		String e = abc.substring(1);
		String f = abc.substring(2);
		System.out.println(d);  //abc
		System.out.println(e);  //bc
		System.out.println(f);  //c
	}
}

<aside> 💁🏻 Returns a new string that is a substring of this string. The substring begins with the character at the specified index and extends to the end of this string.

Examples:

"unhappy".substring(2) returns "happy" "Harbison".substring(3) returns "bison" "emptiness".substring(9) returns "" (an empty string)

</aside>

2️⃣ public String substring(int beginIndex, int endIndex)

<aside> 💁🏻 Returns a string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.

Examples:

"hamburger".substring(4, 8) returns "urge" "smiles".substring(1, 5) returns "mile"

</aside>

출처

🔗 substirng(int beginIndx): https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#substring(int)