1 輸出

System.out.println("Hello World");
System.out.println("First Number = " + firstNumber);
System.out.println("args[" + i + "]: " + args[i]);

2 變量定義

int firstNumber;
long firstNumber;
firstNumber = 10;
double thirdNumber = 10.2d;
char ch = 'a';
boolean value = true;
String greeting = "Hello world!";
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.'};

int[] array1;
array1 = newint[100];
double[] array2 = newdouble[10];
long[] array3= {10L, 23L, 30L, 11L};

Date date = new Date();
SimpleDateFormat ft = new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz");

3 流程控制語句

if (score < 50) {
? ? ? ? ? ? System.out.println("You are not pass");
? ? ? ? }
? ? ? ? else if (score >= 50 && score < 80) {
? ? ? ? ? ? System.out.println("You are pass");
? ? ? ? }
====
if (num1 > num2)
? ? ? result = num1;
? ?else
? ? ? result = num2;
====
? ? ? ? switch (age) {
? ? ? ? case 18:
? ? ? ? ? ? System.out.println("You are 18 year old");
? ? ? ? ? ? break;
? ? ? ? case 20:
? ? ? ? ? ? System.out.println("You are 20 year old");
? ? ? ? ? ? break;
? ? ? ? default:
? ? ? ? ? ? System.out.println("You are not 18 or 20 year old");
? ? ? ? }
====
? ? ? ? for(intvalue = 0; value < 10; value = value + 3) {?
? ? ? ? ? ? System.out.println("Step ="+ step + " ?value = "+ value);
? ? ? ? ? ? step = step + 1;?
? ? ? ? }


? ? ? ? for (int index = 0; index < myArray.length; index++) {
? ? ? ? ? ? System.out.println("Element " + index + " = " + myArray[index]);
? ? ? ? }
====
? ? ? ? while( value < 10) ?{
? ? ? ? ? ? System.out.println("Value = "+ value);
? ? ? ? ? ? value = value + 2;
? ? ? ? }
? ? }


? ? ? ? do {
? ? ? ? ? ? System.out.println("Value = " + value);
? ? ? ? ? ? value = value + 3;
? ? ? ? } while (value < 10);

4 類模板

public class MyFirstJavaProgram {
? ? public static void main(String []args) {
? ? ? ?System.out.println("Hello World");
? ? }
}?
====
package com.xxx;

public class Person {
? ? public String name;

? ? public Person(String persionName) {
? ? ? ? this.name = persionName;
? ? }

? ? public String getName() {
? ? ? ? return this.name;
? ? }
}
====
package com.xxx;
public class FieldSample {
? ? public static int MY_STATIC_FIELD = 100;
? ? public String myValue;
? ? public FieldSample(String myValue) ?{
? ? ? ? this.myValue= myValue;
? ? }

}
====
package com.xxx;

public class MethodSample {
? ? public String text = "Some text";

? ? public MethodSample() ?{

? ? }

? ? public String getText() {
? ? ? ? return this.text;
? ? }


? ? public void setText(String text) {
? ? ? ? this.text = text;
? ? }

? ? public static int sum(int a, int b, int c) {
? ? ? ? int d = ?a + b + c;
? ? ? ? return d;
? ? }
}
====
package com.xxx;

public class FinalFieldExample {
? ? public final int myValue = 100;
? ? public static final long MY_LONG_VALUE = 1234L;
}
====
package com.xxx;

public class Animal {

? ? public Animal() {

? ? }

? ? public void move() {
? ? ? ? System.out.println("Move ...!");
? ? }

? ? public void say() {
? ? ? ? System.out.println("<nothing>");
? ? }

}

Cat.java
package com.xxx;

public class Cat extends Animal {
? ? public void say() {
? ? ? ? System.out.println("I am Cat");
? ? }

}
====
class MyClass {
? ?int x;
? ?
? ?MyClass() {
? ? ? x = 10;
? ?}
}
====

5?

6 導(dǎo)入

import java.util.*;
import java.text.*;
import java.util.Date;
import java.io.*;


import java.io.BufferedReader;?
import java.io.File;?
import java.io.FileInputStream;?
import java.io.FileReader;?
import java.io.IOException;?
import java.io.InputStream;?
import java.io.InputStreamReader;?
import java.io.RandomAccessFile;?
import java.io.Reader;?


import java.util.regex.Matcher;
import java.util.regex.Pattern;

7 正則

? String line = "This order was placed for QT3000! OK?";
? String pattern = "(.*)(\d+)(.*)";


? // Create a Pattern object
? Pattern r = Pattern.compile(pattern);


? // Now create matcher object.
? Matcher m = r.matcher(line);

8 簡單函數(shù)

/** Return the max between two numbers */
public static int max(int num1, int num2) {
? ?int result;
? ?if (num1 > num2)
? ? ? result = num1;
? ?else
? ? ? result = num2;


? ?return result;?
}
====
/** Method to swap two variables */
public static void swap(int n1, int n2) {
? ?int temp = n1;
? ?n1 = n2;
? ?n2 = temp;
}
====

9 文件

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
str = br.readLine();


File f = new File("C:/java/hello");
InputStream f = new FileInputStream(f);


File f = new File("C:/java/hello");
OutputStream f = new FileOutputStream(f);

10 簡單小程序

import java.io.*;

public class fileStreamTest{

? ?public static void main(String args[]){
? ?? ?try{
? ? ? byte bWrite [] = {11,21,3,40,5};
? ? ? OutputStream os = new FileOutputStream("test.txt");
? ? ? for(int x=0; x < bWrite.length ; x++){
? ? ? ? ?os.write( bWrite[x] ); // writes the bytes
? ? ? }
? ? ? os.close();
? ? ?
? ? ? InputStream is = new FileInputStream("test.txt");
? ? ? int size = is.available();

? ? ? for(int i=0; i< size; i++){
? ? ? ? ?System.out.print((char)is.read() + " ?");
? ? ? }
? ? ? is.close();
? ?}catch(IOException e){
? ? ? System.out.print("Exception");
? ?}
? ?}
}
====

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