🌈Java from entry to grave ⭐ study notes ⭐ (1) String Common methods summary 😊 (small white essential knowledge!!

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Strings are widely used in Java programming. In Java, strings are objects. Java provides the String class to create and manipulate strings.

1. The charAt() method

char c = "Mantis shrimp".charAt(1);
System.out.println(c);
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“Mantis shrimp” is an object. You can use a point as long as it’s an object.

2. The compareTo() method

int result1 = "abc".compareTo("abc");
System.out.println(result1);

int result2 = "abc".compareTo("abd");
System.out.println(result2);

int result3 = "abd".compareTo("abc");
System.out.println(result3);
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= =conclusion= =

If the argument string is equal to this string, return the value 0;
If the string is less than the string argument, return a value less than 0;
If this string is greater than the string argument, a value greater than 0 is returned.

The return value is an integer, it is first to compare the size of the corresponding character (ASCII), = = if the first character and the parameters of the first character, end of comparison, the difference between the return to their value = = = = if the first character is equal to the parameters of the first character, with the second character and parameter of the second character comparison = =, And so on until one of the characters being compared or compared ends.

System.out.println("abc".compareTo("cba"));
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Compare the first string, a-c=-2, and return -2

3, contains() method

== is simply to determine whether the preceding string contains the following substring ==

System.out.println("HelloWorld!".contains("Wor"));
System.out.println("http://www.baidu.com".contains("https"));
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4, endsWith() and startsWith() methods

System.out.println("text.txt".endsWith("txt"));
System.out.println("text.txt".endsWith("java"));
System.out.println("text.txt".startsWith("text"));
System.out.println("text.txt".startsWith("test"));
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System.out.println("text.txt".startsWith("text".0));
System.out.println("text.txt".startsWith("test".1));
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The difference between compareTo() and equals()

==equals() Consider case ==

System.out.println("abc".equals("abc"));
System.out.println("abc".equals("aBc"));
System.out.println("abc".equals("bbb"));
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Return true if the given object is equal to the string; Otherwise return false.

**==compareTo() returns the difference between the two, i.e. returns a number; Equals is simpler. It only returns true or false.

Finally, both compareTo() and equals() can determine other basic data types, such as Integer. The Java source code overloads both methods to automatically match methods based on the type of the argument. 🙂 this kind of judgment. = = * *

EqualsIgnoreCase () method

==equalsIgnoreCase() Ignores case ==

System.out.println("abc".equalsIgnoreCase("abc"));
System.out.println("abc".equalsIgnoreCase("ABc"));
System.out.println("abc".equalsIgnoreCase("bbb"));
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7. The getBytes() method

byte[] bytes = "abcde".getBytes();
for (byte b:bytes){
 System.out.println(b);
}
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8. The indexOf () and lastIndexOf() methods

System.out.println("abcdefghygklmn".indexOf("a"));
System.out.println("abcdefghygklmn".indexOf("def"));
System.out.println("abcdefghygklmn".indexOf("l"));
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System.out.println("abcdefgaabbcc".lastIndexOf("a"));
System.out.println("abcdefgaabbcc".lastIndexOf("c"));
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9. IsEmpty () method

System.out.println("".isEmpty());
System.out.println("aaa".isEmpty());
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10. Replace () method

String text = "aaabbbccc";
System.out.println(text.replace("a"."d"));

String param = "Name = Mantis shrimp &age=18&address= Pond";
System.out.println(param.replace("&".":"));
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11, split() method

You can also split them by strings

String str = "2020-08-14";
String[] splits = str.split("-");
	for (String s: splits) {
	    System.out.println(s);
 }

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

 String param = "Name = Mantis shrimp &age=18&address= Pond";
 String[] split = param.split("&");
	for (String s: split) {
	    System.out.println(s);
 }
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12. Substring () method

BeginIndex — Start index (including), index starting from 0.
EndIndex — endIndex (not included).

String text = "http://www.baidu.com";
System.out.println(text.substring(7));
System.out.println(text.substring(0.7));
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13. ToCharArray () method

char[] chars = "Favorite shrimp, mantis shrimp.".toCharArray();
for (char ch:chars){
       System.out.println(ch);
}
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14. ToLowerCase () and toUpperCase() methods

String text = "aaAA";
System.out.println(text.toLowerCase());
System.out.println(text.toUpperCase());
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15, trim() method

== Remove whitespace before and after the string ==

String text = " hello world! ";
System.out.println(text.trim());
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16. The Valueof() method

double d = 1111.11;
boolean b = false;
long l = 123456789;
char[] arr = {'w'.'o'.'r'.'l'.'d'};

System.out.println(Return value: + String.valueOf(d) );
System.out.println(Return value: + String.valueOf(b) );
System.out.println(Return value: + String.valueOf(l) );
System.out.println(Return value: + String.valueOf(arr) );
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The Valueof() layer calls the toString() method

When the argument is an object

When the toString() method is not overridden

public class Main {

    public static void main(String[] args) {
        String s = String.valueOf(newPerson()); System.out.println(s); }}class Person{}Copy the code

== Print memory address ==

Overrides the toString() method

public class Main {

    public static void main(String[] args) {
        String s = String.valueOf(newPerson()); System.out.println(s); }}class Person{
    @Override
    public String toString(a) {
        return "I'm a mantis shrimp."; }}Copy the code

== Prints data returned by toString() ==

16.1, system.out.println () low-level call

Object o = new Object();
System.out.println(o);
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Call the valueOf ()

Call the toString ()

In fact, the system.out.println () method converts any data to a string and then prints it.

The last

I am aCode pipi shrimpI am a mantis shrimp lover who loves to share knowledge. I will keep updating my blog in the future. I look forward to your attention!!

Creation is not easy, if this blog is helpful to you, I hope you can == a key three! ==, thanks for your support, see you next time ~~~