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This article introduces the knowledge of "how to use Eclipse in Java". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Eclipse use introduction to set up encoding

In order to avoid garbled code, change it to UTF-8.

Modify the default workspace

How to import an existing project

This problem occurs:

Because the ".project" file or ".classpath" file does not exist in the folder

Solution: none

How to import a source file

Open source files and ctrl+v the package

There is a garbled problem.

Solution: nodepad++ modifies the code set of the source file

Too many projects, closed project

One workspace corresponds to one configuration

Specific to a certain workspace '.metadata', if some configurations are changed incorrectly and cannot be recovered, the file can be deleted and workspace is classified as initialization.

View the source code

Find the "src.zip" file

Other

Quickly find the source code of the function

Author template shortcut key → / * * line feed

The corresponding template can appear.

Array

Array definition

An ordered collection of data of the same type

Mixed types are not allowed, but array types can be any data type, including base and reference types.

Declaration and initialization of array

How to call an element at a specified location in an array

How to get the length of an array

How to traverse an array

Default initialization values for array elements

Memory parsing of array

Declare, initialize

Int [] s = new int [] {1001meme 1002min1003}; / / static initialization String [] names = new String [5]; / / dynamic initialization

When initialization is complete, the length of the array is determined; and the length cannot be modified.

Int [] s = null; / / when declared, JVM does not allocate space

S = new int [10]; / / the array is created successfully and the length is determined.

Default initialization-the compiler default operation default (applies only to member variables, that is, class members):

Initial value of byte,short,int,long is 0

Float,double is 0.0

Char is'\ u0000' instead of'0'

Boolean type is false (true is 1)

Reference type is null

Call specific location elements

The default subscript starts at 0, but when Java interacts with the database SQL, the subscript starts at 1

Get length

With the help of array properties, length

System.out.println (names.length)

Ergodic mode foreach

Elements designed to read (cannot be modified) an array

Array memory parsing

The memory of Java virtual machine can be divided into three areas: stack Stack, heap Heap, and method area Method area.

The stack is private to threads and cannot be shared between threads!

The stack describes the memory model of method execution; each method is called to create a stack frame (storing local variables, operands, method exits, etc.)

JVM creates a stack for each thread to store information about the thread's execution method (actual parameters, local variables, etc.)

The stack is automatically allocated by the system, the speed is fast, the stack is a continuous memory space.

JVM has only one heap, which is shared by all threads

Heap is used to store created objects and arrays (arrays are also objects, keyword is new)

Heap is a discontiguous memory space with flexible allocation and slow speed.

JVM has only one method area, which is shared by all threads

The method area is actually a heap, which is used to store the immutable or unique content in the program. (class information [class object], static variables, string constants, etc.)

Specific array code analysis:

Understanding of two-dimensional array

The array itself is a reference data type, and the elements of the array can be either a basic data type or a reference data type (continue to be an array)

In essence, an array is also a kind of object. The array of an array only needs to specify the size of the previous array, and the length of the latter array is unlimited.

Int [] arr = new int [] {1 arr 2 arr 3}; int [] 3}; / / Type inference / / 1. Statically initialize int [] [] arr1 = new int [] [] {{1int 2dag3}, {4rect 5}, {6jue 7}}; / / dynamically initialize String [] [] arr2 = new String [3] [2]; String [] [] arr3 = new String [3] []; / / the length can be variable / / 2. Call the array specified position System.out.println (arr1 [0] [1]); / / 2System.out.println (arr2 [1] [1]); / / nullarr3 [1] = new String [4]; / / if not added, the following code will report a null pointer error System.out.println (arr3 [1] [0]); / / null// 3. The length of the array System.out.println (arr1.length); / / 3System.out.println (arr1 [1]. Length); / 2. Traverse for (int I = 0; I < arr2.length; iTunes +) {for (int j = 0; j < arr2 [I] .length; jacks +) {System.out.println (arr [I] [j] + ");} System.out.println ();} / / 5. There are two types of default initialization / *: 1. Int [] [] arr = new int [4] [3]; the initial value of the outer element is: address value the initialization value of the inner layer element is the same as that of the one-dimensional array initialization case 2. Int [] [] arr = new int [4] []; initialization value of the outer element: null Inner layer: cannot call, error * / int [] [] arr4 = new int [4] [3]; System.out.println (arr [0]); / / address value!! [I@15db9742System.out.println (arr [0] [0]); / / 0System.out.println (arr); / / [I@6d06d69c

Memory structure of two-dimensional array:

Sorting algorithm

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