Free learning recommendation: java basic tutorial

• 1. User interaction Scanner
• 2. Sequential structure
• 3. Selection structure
• • • if radio selection structure
    • if double selection structure
    • if multiple selection structure
    • Nested if structure
    • switch multiple selection structure

1. User interaction Scanner

• In the basic syntax we learned before, we did not realize the interaction between programs and people, but Java We are provided with such a tool class that we can obtain user input. java.util.Scanner is a new feature of Java5. We can obtain user input through the Scanner class
• Basic syntax

Scanner?s?=?new?Scanner(System.in);

• Through Scanner The next() and nextLine() methods of the class obtain the input string. Before reading, we generally need to use hasNext() and hasNextLine() to determine whether there is still input data.

Remember to enter scanner.close() at the end of the program to close the scanner and reduce resource usage

2. Sequential structure

• The basic structure of JAVA is the sequential structure. Unless otherwise stated, it will be executed sentence by sentence in order.
• Sequential structure is the simplest structure algorithm.
• Between statements and between boxes are carried out in order from top to bottom. It is composed of several processing steps that are executed in sequence. It is the best choice for any short hair. A basic algorithmic structure that cannot be separated.

3.Select structure

• if single choice structure

We often need to judge whether something is feasible, and then we execute it. Such a process is represented by an if statement in the program

Grammar

if(布爾表達(dá)式){
????//如果布爾表達(dá)式為true將執(zhí)行的語句}

• if double choice structure

Scenario: The company wants to acquire a software, it succeeds: It pays 1 million yuan to someone, it fails : Find someone to develop it yourself.

In this scenario, it is impossible to use an if. We need two judgments and a double selection structure (if-else)

Grammar:

if(布爾表達(dá)式){
????//如果布爾表達(dá)式的值為true}else{
????//如果布爾表達(dá)式的值為false}

• if multiple choice structure

Scenario: Possible real situation Possible There are multiple choices such as ABCD, and there are multi-level judgments in intervals. For example, 90-100 is A, 80-90 is B..., many times in life we ??have more than just two choices, so we need a multi-choice structure to deal with such problems!

Syntax:

if(布爾表達(dá)式1){
????//如果布爾表達(dá)式?1的值為true，則執(zhí)行}else?if(布爾表達(dá)式2){
????//如果布爾表達(dá)式?2的值為true，則執(zhí)行}else?if(布爾表達(dá)式3){
????//如果布爾表達(dá)式?3的值為true，則執(zhí)行}else{
????//如果以上布爾表達(dá)式都不為true，執(zhí)行代碼}

• Nested if structure

It is legal to use nested if...else statements. This means you can use an if or else if statement within another if or else if statement. You can nest else if...else like if statements.

Grammar:

if(布爾表達(dá)式1){
????//如果布爾表達(dá)式?1的值為true，執(zhí)行
????if(布爾表達(dá)式2){
????????//如果布爾表達(dá)式?2的值為true，執(zhí)行
????}}

Thinking? We need to find a number between 1-100 (hint: dichotomy)

• switch multiple selection structure

1. multiple Another implementation of the selection structure is the switch case statement.
2. The switch case statement determines whether a variable is equal to a value in a series of values, and each value becomes a branch.
3. The variable type in the switch statement can be:

• byte, short, int or char
• Starting from Java SE 7, switch The String type is supported
• At the same time, the case label must be a string constant or literal.

switch(expression){
????case?value:
????????//語句
????????break;
????case?value:
????????//語句
????????break;
????//你可以有任意數(shù)量的case語句
????default://可選????????//語句}

##Follow the file to find it We built the package before writing the code and found the class file

We couldn't paste the file directly from IDEA, so we needed to find the folder where the java file was stored and directly Put the class file in

Summary:

• Each object has its own hashCode, each Chinese character has its corresponding hash value, and then IDEA uses the hash value to Judgment and comparison

• After the code is compiled, the bytecode is executed like this (above picture)

• Directly throw the class file to You can view its source code in IDEA (a simple and violent decompilation method). If you want to download some other decompilation tools, you can Baidu

• to see more source code!

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