靜態代碼塊

public class Main {static {System.out.println("測試類的靜態代碼執行");}public static void main(String[] args){Person p1=new Person();Person p2=new Person();} }class Person{static{System.out.println("Person類中靜態代碼塊執行");} }

成員內部類

public class Main {public static void main(String[] args) {outer.inner in = new outer().new inner();in.show();} }class outer {int num = 4;class inner {void show() {System.out.println(num);}} }

內部類

public class Solution {public static void main(String[] args){//定義一個內部類Cat實現Animal接口class Cat implements Animal{public void shout(){System.out.println("喵喵。。。");}}animalShout(new Cat());//調用方法，并傳入對象}private static void animalShout(Animal an) {an.shout();//調用傳入對象的方法} }//定義Animal接口 interface Animal{void shout();//定義抽象方法 }

匿名內部類

public class Solution {public static void main(String[] args){//定義匿名內部類作為參數傳給AnimalShout()方法animalShout(new Animal() {@Overridepublic void shout() {System.out.println("喵喵。。。");}});}private static void animalShout(Animal an) {an.shout();//調用傳入對象的方法} }//定義Animal接口 interface Animal{void shout();//定義抽象方法 }

String類的初始化

public class Main {public static void main(String[] args) throws Exception {// TODO Auto-generated method stubString str1 = new String();String str2 = new String("abcd");char[] charArray = new char[] { 'D', 'E', 'F' };String str3 = new String(charArray);System.out.println("a" + str1 + "b");System.out.println(str2);System.out.println(str2);}}

統計字串的個數

public class Solution {public static void main(String[] args) {String str = "nbaernbatnbaynbauinbaopnba";String key = "nba";int count = getKeyStringCount(str, key);System.out.println(count);}private static int getKeyStringCount(String str, String key) {int count = 0;//if(!str.contains(key))//不包含keyif (str.indexOf(key) == -1)return count;int index = 0;//記錄key出現的位置while ((index = str.indexOf(key)) != -1) {str = str.substring(index + key.length());count++;}return count;}}

定位字符串

public class Main {public static void main(String[] args) throws Exception {// TODO Auto-generated method stubString s = "ababcdedcba";System.out.println(s.length());System.out.println("first index of 'c':" + s.indexOf('c'));System.out.println("last index of 'c':" + s.lastIndexOf('c'));System.out.println("first index of \"ab\":" + s.indexOf("ab"));System.out.println("last index of \"ab\":" + s.lastIndexOf("ab"));}}

字符串的替換和去除空格的操作

import java.util.Arrays;public class Main {public static void main(String[] args) {String s = "itcast";//字符串替換操作System.out.println("將it替換為cn.it:" + s.replace("it", "cn.it"));//字符串去除空格操作String str = " i t c a s t ";System.out.println("去除字符串兩端的空格：" + str.trim());System.out.println("去除字符串所有的空格：" + str.replace(" ", ""));} }

字符串判斷操作

import java.util.Arrays;public class Main {public static void main(String[] args) {String s1 = "string", s2 = "str", s3 = "string";System.out.println("判斷是否以str開頭：" + s1.startsWith("str"));System.out.println("判斷是否是以ng結尾：" + s1.endsWith("ng"));System.out.println("判斷是否包含字符串abc："+s1.contains("abc"));System.out.println("判斷兩個字符串是否相等："+s2.equals(s1));} }

獲取系統全部屬性

import java.util.*; public class Main {public static void main(String[] args) throws Exception {// TODO Auto-generated method stub//獲取當前系統屬性Properties properties=System.getProperties();System.out.println(properties);System.exit(0);//停止運行System.exit(1);//非0標識異常退出//獲取所有系統屬性的key(屬性名)，返回SET對象Set<String> propertyNames=properties.stringPropertyNames();for(String key:propertyNames) {//獲取當前鍵key（屬性名）所對應的值（屬性值）String value =System.getProperty(key);System.out.println(key+"------>"+value);}}}

獲取時間和數組拷貝

import java.util.*; public class Main {public static void main(String[] args) throws Exception {// TODO Auto-generated method stublong startTime=System.currentTimeMillis();//循環開始的當前時間int sum=0;for(int i=0;i<(int)1e9;i++) {sum+=i;}long endTime=System.currentTimeMillis();System.out.println((endTime-startTime)+"毫秒");int[] fromArray= {10,20,30};int[] toArray=new int[10];System.arraycopy(fromArray, 0, toArray, 1, 3);System.out.println(Arrays.toString(toArray));} }

虛擬機運行時的狀態

import java.util.*;public class Main {public static void main(String[] args) throws Exception {// TODO Auto-generated method stubRuntime rt = Runtime.getRuntime();//獲取虛擬機運行的狀態System.out.println("處理器的個數：" + rt.availableProcessors());System.out.println("空閑內存大小：" + rt.freeMemory() / 1024 / 1024 + "MB");System.out.println("最大可用內存數量：" + rt.maxMemory() / 1024 / 1024 + "MB");rt.exec("notepad.exe");//命令打開一個記事本程序Process process = rt.exec("notepad.exe");//得到表示進程的Process對象Thread.sleep(3000);//程序休眠3秒process.destroy();//殺掉進程} }

Iterator接口

import java.util.*;public class Main {public static void main(String[] args) throws Exception {ArrayList list = new ArrayList();list.add("data_1");list.add("data_2");list.add("data_3");//遍歷方法1：Iterator接口Iterator it = list.iterator();//獲取Iterator對象while (it.hasNext()) {Object obj = it.next();System.out.println(obj);}//遍歷方法2:foreach循環/*foreach(容器中元素類型 臨時變量：容器變量){執行語句}*/for (Object obj : list) {System.out.println(obj);}} }

HashSet集合

import java.util.*;public class Main {public static void main(String[] args) throws Exception {HashSet set = new HashSet();for (int i = 1; i <= 5; i++) {set.add(i);set.add(i);//添加重復元素}Iterator it = set.iterator();while (it.hasNext()) {//判斷是否有重復元素Object obj = it.next();System.out.println(obj);}} }

HashMap集合

import java.util.*;public class Main {public static void main(String[] args) throws Exception {Map map = new HashMap();//創建Map集合map.put("1", "Jack");map.put("2", "Rose");map.put("3", "Luck");map.put("3", "Tom");//覆蓋Set keySet = map.keySet();//獲取鍵的集合Iterator it = keySet.iterator();//迭代鍵的集合while (it.hasNext()) {Object key = it.next();Object value = map.get(key);//獲取每個鍵所對應的值System.out.println(key + ": " + value);}} }

Java類型轉換

public class Main {public static void main(String[] args) {String s1 = "0.5", s2 = "12";double x = Double.parseDouble(s1);//將字符串S1變成double類型int y = Integer.parseInt(s2);//將字符串S2變成int類型System.out.println(x + y);//x+y=12.5} }

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