Small knowledge of common classes

Boxing and UnBoxing

Boxing turns basic types into reference types
Unpacking changes the reference type to the basic type

        int age=30;
        // Automatic boxing 
        Integer integer4=age;
        // Automatic dismantling 
        int age2 =integer4;

Basic type and string conversion

 //1, The basic type is converted to a string 
        int n1=10;
        String n2= n1+"";
        // Use Integer Medium toString() Method 
        String s2=Integer.toString(n1);
        //toString  Overload method of  n1 With 16 Hexadecimal said 
        String s3=Integer.toString(n1,16);
    
        //2, String to base type 
        String s1="yan";
  // Use integer2.parseInt() Method put int The type changes to String type 
        int n3=integer2.parseInt(s1);
        
  //boolean The string form is changed to the basic type :"true"-->true, Not true-->false
        String str2="true";
        boolean bl=Boolean.parseBoolean(str2);

== and equals

== When comparing two basic types , Compare values
The comparison is that the reference type is , The comparison is the address

equals stay Object Class compares addresses
String Class overridden equals Method , stay String Next equals Compare values

Integer buffer

//Integer The number stored in the buffer is -128 To 127 The array between is stored in the heap 
        // Recreate storage space beyond the scope 
        Integer integer1=Integer.valueOf(100);
        Integer integer2=Integer.valueOf(100);
        System.out.println(integer1==integer2);
        //true
        Integer integer6=new Integer(200);
        Integer integer7=new Integer(200);
        System.out.println(integer6==integer7);
        //false

String Method

String content =" kankanshijie ";
        System.out.println(content.length()); // Returns the length of the string 
        System.out.println(content.charAt(0));  // Get the current character according to the subscript 
        System.out.println(content.contains("iji"));  // Determine if the string contains "" String inside 
        System.out.println(Arrays.toString(content.toCharArray()));
        //content.toCharArray() The address of the current string is printed 
        //Arrays.toString Print the string of the current address 
        System.out.println(content.trim()); // Remove the space before and after the string 
        System.out.println(content.toUpperCase()); // Become capital 
        System.out.println(content.toLowerCase());// Become lowercase 
        System.out.println(content.replace("kank","wod"));
        // Replace the specified string with the desired string 
        System.out.println(Arrays.toString(content.split("ka")));


        // Split string 
        String say="java is the best programing ,My Language";
        String []arr=say.split("[, ]+");  // Inside the brackets is the judgment of what to split. Here are spaces and commas 
        System.out.println(arr.length);  // Print array length 
        for(String string:arr){
    
            System.out.println(string);  // Print the string in the array 
        }

        // Compare the position of two strings in the table and subtract , From the first , If the same, compare the next 
       //  If the two preceding characters are the same , Just compare the length of two strings 
        // Can be used for sorting 
        String s1="abc";
        String s2="xyz";
        System.out.println(s1.compareTo(s2));