package com.bjpowernode.java_learning;

​

public class D74_1_StringCommonMethod {

  public static void main(String[] args) {

    //1.转为大写

    System.out.println("Abhdugfi".toUpperCase());

    //2.转换为小写

    System.out.println("AHUJGjhid".toLowerCase());

    //3.去除字符串前后的 空白

    System.out.println("     a    bcd d e     ".trim());

    //4.String valueOf(Object obj);

    Object o = new Object();

    o = null;

    System.out.println(o);//不会出现空指针异常，因为这里并不是直接调用toString方法，String.valueOf(Object)这个方法对空值进行处理了

    System.out.println(String.valueOf(o));

    //System.out.println(o.toString());//这条语句会出现空指针异常

  }

​

}

package com.bjpowernode.java_learning;

​

public class D74_2_RegularExpression {

  public static void main(String[] args) {

    String s1 = "hjifnasoodjhousnrdgoihjfviodjfg465ds46g51fdsg";

    //将ji替换成“中”

    System.out.println(s1.replaceAll("ji","中"));

    //将oo转换为“国”

    System.out.println(s1.replaceAll("o{2}", "国"));

    //将数字替换为“人”

    System.out.println(s1.replaceAll("\\d","人"));

  }

​

}