Scjp review notes (2)

 

Example 11:

Note the usage of length and length (): for example, string STR = "My name is wuyangping" is used to evaluate the length to Str. length (); but string [] STR = new string [5], the length of this is str. length.

Example 12:

The output input format in Java is also supported. For example, system. Out. printf ("Pi is approximately % F and E is approximately % B", math. Pi, math. E );

The output result is: PI is approximately 3.141593 and E is approximately true.

Example 12:

Public class beat {

Integer I; // Line 2

Int X;

Public beat (INT y ){

X = I + Y; // line 5

System. out. println (x );

}

Public static void main (String [] args ){

New Beat (new Integer (4); // line 9

}

}

NullPointException exception occurs during I compilation in Line 2. Change it to Integer I = new Integer (1.

Example 13:

This introduces the object-oriented design. From Chapter 1, the difficulty was quickly increased, and the number of questions in each chapter began to increase. When encountering an inherited or multi-type question, be sure:

Step 01: roughly draw a category Chart Based on the program.

Step 02: Check whether the parent category provides a parameter-free constructor. If no parameter constructor exists, the subcategory should

Call super (Hangzhou) or this (...) in the second line of the constructor (...). If no super (callback) or

This (...) should cause compilation to fail!

Step 03: Check whether the overwriting method meets the rules (see section 9-4: overwriting method).

Step 04: Check whether multiple types are used (variables or parameters declared with upper-layer types are used to refer to lower-layer types

Object created ). If multiple models are used, pay attention to whether the called method covers the quilt category.

Step 05: if there is a transformation in the program, check whether there will be execution errors.

In this way, the problem solving or inspection program should be able to obtain results.

Example 14:
The naming rules for JavaBean are setXXX (), getXXX (), and isXXX ();

Example 15:

Class Foo {

Public int a = 3;

Public void addFive () {a + = 5; System. out. print ("f ");}

}

Class Bar extends Foo {

Public int a = 8;

Public void addFive () {this. a + = 5; System. out. print ("B ");}

}

Public class Person {

Public static void main (string d []) {

Foo F = new bar ();

F. addfive ();

System. Out. println (F. );

}

}

The output is B 3. F. A calls the method of the parent class.