Common methods of string class

String explain ：

String Declare as final, Not to be inherited ;

String Realized Serializebla Interface , Indicates that the string supports serialization ;

String Realized Comparable Interface , indicate String It can be compared in size ;

Assign a value to the string by literal way , At this point, the string value is declared in the string constant pool （ Strings with the same content will not be stored in the string constant pool ）

String Represents an immutable sequence of characters , Have no variability

• After reassigning the string constant , You need to re assign values in the specified memory area , Can't be on the original value Modify assignment directly
• When connecting strings , You need to re assign values in the specified memory area , Can't be on the original value Operate directly
• When using replace() Method to replace a character or string , You also need to re assign values in the specified memory area , Can't be on the original value Operate directly

Literal and constructor creation String The difference between

public class StringTest {
    @Test
    public void test(){
        // Literal declaration string ：s And s1 The data of is placed in the string constant pool 
        String s = "hello";
        String s1 = "hello";
        System.out.println(s==s1);  //true   The same data value in the constant pool 
        //new +  The way constructors are ：s2 And s3 Saved address values , Is the address value corresponding to the data after opening up space in the heap space 
        String s2 = new String("yes");
        String s3 = new String("no");
        System.out.println(s2==s3);// Point to different address values in the heap 
    }
}

Connect constants with constants , The result is in the constant pool ; As long as one of the connection operations is a variable , The result is in heap space ;

String Common methods ：

 

 

        //String --> char[]  call String Of toCharArray() Method 
        String s4 = "hello";
        char[] c = s4.toCharArray();
        for (int i = 0; i < c.length; i++) {
            System.out.println(c[i]);
        }
        //char[] --> String   call String Constructor 
        char[] c1 = new char[]{'w','o','r','l','d'};
        String s5 = new String(c1);
        System.out.println(s5);


        //String --> byte[]   call String Of getBytes() Method 
        String s6 = "abc";
        byte[] b = s6.getBytes();
        System.out.println(Arrays.toString(b));  // [97, 98, 99]

 

public class String1{
    public static void main(String[] args) {
        /*
        String str = "hello";
        1  Intercept out str First character of 
        char c = str.charAt(0);

        char[] data = str.toCharArray();  // take str Converts a string to an array of characters 
        for (int i = 0; i<data.length; i++){
            System.out.println(data[i]);
        }
       */

/*
        2  Given a string , Judge whether it is composed of numbers 
        String str = "1234o847290";
        if (isNumber(str)){
            System.out.println(" A string consists of numbers ");
        }else{
            System.out.println(" A string consists of non numbers ");
        }
    }
    public static Boolean isNumber(String str){  // Declare the main class method as static, You can use this method directly in the main class , There is no need to declare objects 
        char[] data = str.toCharArray();
        for (int i =0; i<data.length; i++){
            if (data[i] <'0' || data[i]>'9'){
                return false;
            }
        }
        return true;
*/

        /* 3  String comparison 
        String str1 = "helloworld";
        String str2 = "HelloWorld";
        System.out.println(str1.equals(str2));   //  Distinguish case and compare whether two strings are equal 
        System.out.println(str1.equalsIgnoreCase(str2));   // Case insensitive comparison of two strings for equality 
        System.out.println(str2.compareTo(str1));  // Compare the relationship between two strings , The result is greater than 0, Less than 0, Or equal to 0
        */
/*
        //4  String truncation 
        String str = "anbdjhd";
        String s1 = str.substring(3);     // Truncate from the specified index to the end 
        String s2 = str.substring(0,4);  // Partial intercept [0,4)
        System.out.println(s1+"\t"+s2);
 */
        /*
        //5  String splitting 
        String str = "hello world you me he";
        String result1[] = str.split(" "); // Split with spaces 
        String result2[] = str.split(""); // Split all strings 
        System.out.println(result2[6]);
        */

        // Determine if it is an empty string  strName.isEmpty()
        String str = "abdbud";
        String str1 = "";
        System.out.println(str.isEmpty());  //false  Non empty 
        System.out.println(str1.isEmpty());  //true  empty 
        System.out.println(initcap(str));  // Realize the capitalization of the first letter of a string 
    }
    // Capitalize the first letter , Defined as static type , You can call directly in the main class 
    public static String initcap(String str){
        // First convert the initial letter to uppercase and then add the following string 
        String temp = str.substring(0,1).toUpperCase() + str.substring(1);
        return temp;
    }
}