String StringBuilder StringBuffer "..." 4种的效率-优快云博客

本文通过实验对比了Java中不同字符串拼接方式的性能表现，包括直接拼接、使用StringBuilder、StringBuffer及String对象的方式，并提供了详细的测试代码。

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"..." +"..." 直接字面值的操作最快，因为 jvm 直接将其解释为 1个字符串

String 对象的操作比较耗费时间，

StringBuilder 还可以，非线程安全的

StringBuffer 还行，线程安全，比 StringBuilder 慢点，

大多数情况下，效率上：

"..." + "..." > StringBuilder > StringBuffer > String对象+String对象

测试类：

package test;

public class StringAddTest {
	private final static int repeatCount = 10000000;

	public void testStringDirect() {
		long begin = System.currentTimeMillis();
		for (int i = 0; i < repeatCount; i++) {
			String s = "abc" + "_opq_" + "xyz";
		}
		long over = System.currentTimeMillis();
		System.out.println("\"...\"+\"...\" 直接相加：" + (over - begin) + " millseconds ");
	}

	public void testStringBuffer() {
		long begin = System.currentTimeMillis();
		for (int i = 0; i < repeatCount; i++) {
			StringBuffer s = new StringBuffer();
			s.append("abc").append("_opq_").append("xyz");
		}
		long over = System.currentTimeMillis();
		System.out.println("StringBuffer 的 append() ： " + (over - begin) + " millseconds ");
	}

	public void testStringBuilder() {
		long begin = System.currentTimeMillis();
		for (int i = 0; i < repeatCount; i++) {
			StringBuilder s = new StringBuilder();
			s.append("abc").append("_opq_").append("xyz");
		}
		long over = System.currentTimeMillis();
		System.out.println("StringBuilder 的 append() ： " + (over - begin) + " millseconds ");
	}

	public void testStringObject() {
		long begin = System.currentTimeMillis();
		for (int i = 0; i < repeatCount; i++) {
			String s1 = "abc";
			String s2 = "_opq_";
			String s3 = "xyz";
			String s = s1 + s2 + s3;
		}
		long over = System.currentTimeMillis();
		System.out.println("String 对象 相加， 直接相加：" + (over - begin) + " millseconds ");
	}

	public static void main(String[] args) {
		StringAddTest st = new StringAddTest();
		st.testStringDirect();
		st.testStringBuffer();
		st.testStringBuilder();
		st.testStringObject();
	}
}