Class initialization

Create a class using the new keyword and initialize it by calling the constructor of the class. Constructors can assign values to attributes of a class.

Member variables

Member variables: outside methods, inside classes. Also a class attribute

Note the default values of member variables when they are not assigned.==String is also an object with an initial default value of NULL ==

Static properties, static code blocks, normal properties, normal methods, normal method blocks, constructor initialization order

  • Static properties: Properties that are static
  • Static method blocks: blocks of code included in static{}
  • Normal properties: properties that are not static (call method output tests for effect)
  • Normal method blocks: blocks of code included in {}
  • Constructor: Method with the same class name, used to initialize the method
  • Methods: Normal methods that are effective when called
public class LifeCycle {
    // Static properties
    private static String staticField = getStaticField();

    // Static code block
    static {
        System.out.println("StaticField:" + staticField);
        System.out.println("2: Static code block");
    }

    // Common properties are initialized by calling the spectrum method
    private String field =getField();

    // Common method block
    {
        System.out.println("4: Normal method block initializes field:" + field);
    }
    private String getField(a) {
        System.out.println("3: Normal properties");
        return "field";
    }
    private static String getStaticField(a) {
        System.out.println("1: Static properties");
        return "staticField";
    }
    // The constructor
    public LifeCycle (a){
        System.out.println("5: Constructor initialization");
    }
    public static void main(String[] args) {
        newLifeCycle(); }}Copy the code

Execution result:

1: static attribute staticField: staticField2: Static code block3: Common property4: normal method block initializes field:field5The: constructor is initializedCopy the code

Initialization of an array

int[] a; Or generally use the followingint a[];
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Direct assignmentint array[3] = {1.2.3}; The third value of partial assignment isintThe default value of0
int array[3] = {1.2}; The assignment parameter determines the length of the array. The length of the next example is2
int array[] = {1.2};
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Variable parameter method

public int add (int. numbers){
	int sum = 0;
	for(int num : numbers){
		sum+=num;
	}
	returnsum; } call method add();// No parameter is passed
add(1); // One parameter
add(1.2); // Two parameters
add(new Integer[]{1.2.3.4}); // Pass the array


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