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本文链接:https://blog.csdn.net/weixin_42528266/article/details/102961917
包装类均位于java.lang包,包装类和基本数据类型的对应关系:
代码示例
package com.cwl.base.day04.boxing;
/**
* @program: java_base
* @description: 测试包装类的基本用法
* @author: ChenWenLong
* @create: 2019-11-08 09:28
**/
public class Test01 {
public static void main(String[] args) {
Integer i = new Integer(1000);
System.out.println(Integer.MAX_VALUE);
System.out.println(Integer.toHexString(i));
Integer i2 = Integer.parseInt("234");
Integer i3 = new Integer("333");
System.out.println(i2.intValue());
String str = 234+"";
}
}
Integer i = 100;
Integer i = Integer.valueOf(100);
int a = new Integer(100);
int a = new Integer(100).intValue();
代码示例
package com.cwl.base.day04.boxing;
/**
* @program: java_base
* @description: 测试自动装箱和拆箱
* @author: ChenWenLong
* @create: 2019-11-08 09:28
**/
public class Test02 {
public static void main(String[] args) {
// Integer a = new Integer(1000);
Integer a = 1000; //jdk5.0之后 . 自动装箱,编译器帮我们改进代码:Integer a = new Integer(1000);
Integer b = null;
int c = b; //自动拆箱,编译器改进:b.intValue();
System.out.println(c);
Integer d = 1234;
Integer d2 = 1234;
System.out.println(d==d2);
System.out.println(d.equals(d2));
System.out.println("###################");
Integer d3 = -100; //[-128,127]之间的数,仍然当做基本数据类型来处理。
Integer d4 = -100;
System.out.println(d3==d4);
System.out.println(d3.equals(d4));
}
}
String s1 = “Hello”;String s2 = “World!”;
String s = s1 + s2; //HelloWorld!
代码示例
package com.cwl.base.day04.string;
/**
* @program: java_base
* @description:
* @author: ChenWenLong
* @create: 2019-11-07 20:01
**/
public class TestString {
public static void main(String[] args) {
String str = new String("abcd");
String str2 = new String("abcd");
System.out.println(str2.equals(str)); //比较内容是否相等。
System.out.println(str2==str);
System.out.println(str.charAt(2));
String str3 = "def";
String str4 = "def";
System.out.println(str3.equals(str4));
System.out.println(str3==str4);
System.out.println(str3.indexOf('y'));
String s = str3.substring(0);
System.out.println(s);
String str5 = str3.replace('e', '*');
System.out.println(str5);
String str6 = "abcde,rrtt,cccee";
String[] strArray = str6.split(",");
for(int i=0;i<strArray.length;i++){
System.out.println(strArray[i]);
}
String str7 = " aa bb ";
String str77 = str7.trim();
System.out.println(str77.length());
System.out.println("Abc".equalsIgnoreCase("abc"));
System.out.println("Abcbd".indexOf('b'));
System.out.println("Abcbd".lastIndexOf('b'));
System.out.println("Abcbd".startsWith("Ab"));
System.out.println("Abcbd".endsWith("bd"));
System.out.println("Abcbd".toLowerCase());
System.out.println("Abcbd".toUpperCase());
System.out.println("##################");
String gh = new String("a");
for (int i = 0; i < 1000; i++) {
gh = gh + i;
}
System.out.println(gh);
}
}