String的用法——判断功能

package cn.itcast_03;

/*

• String的判断功能：

•  1.boolean equals(Object obj):字符串的内容是否相同，区分大小写
  

•  2.boolean equalsIgnoreCase(String str):比较字符串的内容是否相同，忽略大小写
  

•  3.boolean contains(String str)：判断大字符串中是否包含小字符串
  

•  4.boolean startsWith(String str)：判断字符串是否以某个指定的字符串开始
  

•  5.boolean endsWith(String str)：判断字符串是否以摸个指定的字符串结尾
  

•  6.boolean isEmpty()：判断字符串是否为空
  

• 注意：

•  字符串为空和字符串对象为空不一样。
  

•  String s = "";字符串为空
  

•  String s = null;字符串对象为空
  

*/

public class StringDemo {

public static void main(String[] args) {
	//创建对象
	String s1 = "helloworld";
	String s2 = "helloworld";
	String s3 = "HelloWorld";
	String s4 = "hell";

	//boolean equals(Object obj):字符串的内容是否相同，区分大小写
	System.out.println("equals:" + s1.equals(s2));//true
	System.out.println("equals:" + s1.equals(s3));//false
	System.out.println("------------------------------------------------");

	//boolean equalsIgnoreCase(String str):比较字符串的内容是否相同，忽略大小写
	System.out.println("equalsIgnoreCase:" + s1.equalsIgnoreCase(s2));//true
	System.out.println("equalsIgnoreCase:" + s1.equalsIgnoreCase(s3));//true
	System.out.println("------------------------------------------------");

	//boolean contains(String str)：判断大字符串中是否包含小字符串
	System.out.println("contains:" + s1.contains("hell"));//true
	System.out.println("contains:" + s1.contains("hw"));//false,字符必须是连在一起的
	System.out.println("contains:" + s1.contains("owo"));//true
	System.out.println("contains:" + s1.contains(s4));//true
	System.out.println("------------------------------------------------");

	//boolean startsWith(String str)：判断字符串是否以某个指定的字符串开始
	System.out.println("startsWith:" + s1.startsWith("h"));//true
	System.out.println("startsWith:" + s1.startsWith(s4));//true
	System.out.println("startsWith:" + s1.startsWith("world"));//false
	System.out.println("------------------------------------------------");

	//boolean endsWith(String str)：判断字符串是否以摸个指定的字符串结尾
	System.out.println("endsWith:" + s1.endsWith("h"));//false
	System.out.println("endsWith:" + s1.endsWith(s4));//false
	System.out.println("endsWith:" + s1.endsWith("world"));//true
	System.out.println("------------------------------------------------");

	//boolean isEmpty()：判断字符串是否为空
	System.out.println("isEmpty:" + s1.isEmpty());//false

	String s5 = "";
	String s6 = null;
	System.out.println("isEmpty:" + s5.isEmpty());//true
	//对象都不存在，所以不能调用方法
	System.out.println("isEmpty:" + s6.isEmpty());//NullPointerException

}

}