Common methods of string class

About String Construction method of class

1. String s = new String（”“）;
2. String s = ”“; The most commonly used
3. String s = new String (char Array )
4. String s = new String ( char Array , Start subscript , length )
5. String s = new String(byte Array )
6. String s = new String(byte Array , Start subscript , length )
   Code as follows :

        //  Here we only master the common construction methods 
        //  One of the most common ways to create string objects 
        String s1 = "hello world!";
        // s1 It stores a memory address , It is supposed to output an address 
        //  But output a string , explain String The class has been rewritten toString Method 
        System.out.println(s1);
        //  Only the most common construction methods are mastered here 
        byte[] bytes = {
    97,98,99}; // 97 yes a,98 yes b,99 yes c(byte Arrays do these conversions automatically )
        String s2 = new String(bytes); //  Pass a byte Array 
        //  As I said before : When outputting a reference , Automatically called toString() Method 
        //  Default Object Words , The memory address of the object will be automatically output 
        //  Through the output results, we come to a conclusion : String The class has been rewritten toString() Method 
        //  If you output a string object , The output is not the memory address of the object , It's the string itself 
        System.out.println(s2); // abc
        // String( Byte array , The starting position of the subscript of the array element , length )
        //  take byte Part of the array is converted into a string 
        String s3 = new String(bytes,1,2);
        System.out.println(s3); // bc
        //  take char All arrays are converted into strings 
        char[] chars = {
    ' I ',' yes ',' in ',' countries ',' people '};
        String s4 = new String(chars);
        System.out.println(s4);
        //  take char Convert a part of the array into a string 
        String s5 = new String(chars,2,3);
        System.out.println(s5);
        String s6 = new String("hello world!");
        System.out.println(s6);

About String Common methods of class

String Class is often used in business , It is recommended to master , But you can also query API Document to solve ！

public class StringTest05 {
    
    public static void main(String[] args) {
    
        // String Common methods in classes 
        // charAt(int index) //  Put back the char value 
        char c = " Chinese ".charAt(1); // " Chinese " Is a string string object . As long as it's an object "."
        System.out.println(c); //  countries 

        // 2 ( understand ) .int compareTo(String anotherString)
        //  Compare... In dictionary order 
        int result = "abc".compareTo("abc");
        System.out.println(result); //0( be equal to 0)  coherence 

        int result2 = "abcd".compareTo("abce");
        System.out.println(result2); //-1( Less than 0) Small in front and big in back 

        int result3 = "abce".compareTo("abcd");
        System.out.println(result3); //1( Less than 0) Big in front and small in back 

        //  Compare the first letter of the string with the first letter of the following string . There is no comparison between victory and defeat .
        System.out.println("xyz".compareTo("yxz")); // -1

        // 3 ( master ) .boolean contains(CharSequence s)
        System.out.println("hello world".contains("hello"));

        // 4（ master ） boolean endsWith()
        //  Determine whether the current string ends with a string 
        System.out.println("test.txt".endsWith(".java")); // false
        System.out.println("test.txt".endsWith("xt")); // true

        // 5( master ) .boolean equals(Object object)
        //  To compare two strings, you must use equals Method , Out of commission "=="
        //  The underlying comparison principle is to take out characters one by one for comparison 
        // equals Methods can only tell if they are equal 
        // compareTo The method can also tell who is big and who is small 
        System.out.println("abc".equals("abc"));

        // 6.equalsIgnoreCase(String anotherString)  Judge whether two strings are equal, ignore case 
        System.out.println("Abc".equalsIgnoreCase("abc"));
        // 7.( master ).byte[] getBytes()
        //  Convert a string object into a byte array 
        byte[] bytes = "abcdef".getBytes();
        for (byte s:
             bytes) {
    
            System.out.println(s);
        }
        // 8.indexOf(int ch)
        // Returns the index in the string where the specified character first appears .
        System.out.println("helloworld".indexOf("world"));

        // 9. Determine whether a string is empty  .boolean isEmpty()  The underlying source code should call the string length
        System.out.println(" ".isEmpty());
        // 10.int length()
        //  Interview questions :  The length of the judgment array is different from that of the judgment string 
        //  Determine the length of the array is length attribute , Determine the length of the string is length() Method 
        System.out.println("abc".length());

        // 11.lastIndexOf(int ch)  Returns the index of the last occurrence of a substring in the current string ( Subscript )
        System.out.println("hellohelloworldwor;ld".lastIndexOf("wor"));

        // 12.replace(CharSequence target, CharSequence replacement)
        //  Use... In the current string replacement Replace... In the current string target
        // String The parent interface of is : CharSequence
        String newString = "http://www.baidu.com".replace("http://", "https://");
        System.out.println(newString);
        // 13.String[] split(String regex)
        //  Split string 
        String[] split = "1980-10-11".split("-"); //  With  -  Split string for delimiter 
        for (String s:
             split) {
    
            System.out.println(s);
        }

        // 14.startsWith(String prefix)
        //  Determine whether the current string starts with a string 
        System.out.println("hello world".startsWith("hello")); // true
        System.out.println("hello world".startsWith("hellh")); // false

        // 15.substring(int beginIndex) //  The parameter is the starting subscript 
        //  Intercepting string 
        System.out.println("https://www.baidu.com".substring(7)); //  From index to 7 Start intercepting the string at the position of 

        // 16.String substring(int beginIndex,int endIndex)  Start and end subscripts 
        //  Intercepting string 
        System.out.println("https://www.baidu.com".substring(8,15)); //  Left closed right away 

        // 17.char[] toCharArray()
        //  Converts a string to char Array 
        char[] chars = " I'm Chinese ".toCharArray();
        for (char s1:chars){
    
            System.out.println(s1);
        }

        // 18.String toLowerCase()
        //  Convert string to lowercase 
        System.out.println("HELLO WORLD".toLowerCase());

        // 19.String toUpperCase()
        //  Convert strings to uppercase 
        System.out.println("hello world".toLowerCase());

        // 20.String trim()
        //  Remove strings   Before and after   The blank of 
        System.out.println(" hello world ".trim());
        // .String Only one method in is static , Unwanted new object 
        // 21. This method is called valueOf  effect :  take ” The string “ convert to " character string "
        String s1 = String.valueOf(true);
        System.out.println(s1);

        String s2 = String.valueOf(new Customer());
        System.out.println(s2); //  No rewriting toString The object memory address is printed before the , Because of the call toString The method is the parent class Object Class toString Method 

        //  Look at the println() Method source code 
        System.out.println(100);
        System.out.println(3.14);
        System.out.println(true);

        Object o = new Object();
        //  You can see from the source code that :  Why do I output a reference , Would call toString() Method 
        //  Essentially System.out.println() This method   In essence, the target is converted into a string and then output 
        System.out.println(o);

    }
}
class Customer{
     //  No rewriting toString Method   Would call Object Class toString Method   What you print is the address 

    @Override
    public String toString() {
    
        return "Customer{}";
    }
}